@RosinedUp:  I'd say the "#1 rule" from a hypothetical list of rules that actually matter, would be "If you like it, then it is good and doesn't need changed". 

My own Mendini.. Well, right out of the box, I actually had to wonder if I could get a better sound from putting the strings on a cardboard box and bowing them.  In other words, I wasn't particularly happy with the sound.  As I went over learning some of the points of setup, I found things that definitely appeared to be "out' or at least not as right as I felt I could have made them.  As those things were adjusted and corrected, the instrument played better and I liked the sound better.  Some of the changes I made would have been reversible, if they had been mistakes, and some (like taking the thick paint off the fingerboard and shaping the nut) less so. 

To put the bridge in position at what is usually considered the right place?  Well, if I didn't like the sound better I could put it back.  Not much risk there.  When I adjusted the afterlength, I took closeup pics of the adjuster collars on the tailgut so I could put it back if that move ended up being a mistake. 

My thought was that the instrument had been made and adjusted by other humans.  Maybe they knew something I didn't.. and maybe not.  In any case, they would definitely have been trying to make a certain number of instruments a day that were enough like violins to sell.  I wanted an instrument to play.  My "TLC" factor would definitely be higher.  With other stringed instruments like guitars, I have a good track record.  I and others usually feel they play/sound better after I work on them.  Some friends over the years have brought brand new instruments (not all cheap) before they even try playing them so I can "give it the works".  I'll go over it and look for anything that wasn't done quite right, do some assorted things to get a bit better action or sound, that sort of thing.  So I have a certain amount of faith in my own abilities and was willing to risk trying some things with my violins.

But if it sounds and plays like you want, messing with it may be too much of a risk.  Especially if it is the only violin you have.  Might want to get a cheaper one or put in some affordable bids on used "basket case" instruments, if you just want to experiment.  I find such work fascinating and enjoyable, but maybe most people don't.  LOL

@ratvn:  Hard to say how long that may take so settle after such work.  Too many parameters.  But if the varnish was retouching, rather than actually something that could soak into bare wood, then the plates should have kept most of any "playing in" effect they got over the years.  Water and shampoo may not be great for wood, but I actually think that what is affected the most by "settling" and "playing in" is a factor of flexibility on the top and bottom plates that was gained from them being flexed a certain amount and in certain directions while being played so the wood can react better to the vibrations of sound when playing.  That is theory, mind you.  Also a piece of wood that is washed, unless maybe it was left to soak, the rosin content and hardness may not be affected so much as one might think. 

"Cheap glue"?  Well, hide glue *is* a cheap glue, and it is the standard.  In fact, it isn't even actually a great glue, so far as we'd usually think of glue for other things.  It can break pretty easy.  That can be good, because seams like you spoke of, the glue will let go before the wood is damaged.  That is one of the reasons it is used in some musical instruments.  Other glues might not, or they may dampen vibrations differently, which could be either good or bad.

Now, so far as the afterlength tuning being maybe only (or at least more) for gut string.  I have never played on gut strings.  Not yet anyway, it is definitely on my list of things to try someday in the future.  I can't say for certain that synthetic core strings get the same effect from the afterlength being tuned.  I can say, however, that it is physically possible to tune the afterlength so that the afterlength of the D string is in tune with the harmonic on the A string as I described, even with fine tuners in place.  It definitely makes some changes.  From the few instruments I have had to try it on, I noted two effects that I personally felt were desirable from it. 

The first is fairly easy to notice.  The vibrations through the instrument when playing are stronger.  The instrument will "ring" more, in the sense of notes played exciting related notes on other strings, resulting a bit of "sustain" or "echo" when you abruptly stop bowing.  That is, from what I understand, a desirable effect in violins, as it is in guitars.  It makes note transitions sound a bit smoother and gives a stronger sound.

The second is more subtle.  If you bow while sliding your finger that is down on a string up and down the neck very slowly, you may notice that some spots on the neck are a bit louder than others or "sweeter".  If you are a tactile sort of person when it comes to instruments, you may even be able to feel those strong spots when you find them.  As I messed with the afterlength, I noticed that those spots seemed to move.  As I got it close to right, the spots moved to places on the neck where we finger notes, rather than sort of random locations.  So I think I had a bit of an "Ah-HA!" moment and perhaps got the understanding that this instrument is a bit more ingenious and complex than it first appears.  I find that on the instruments where I tuned the afterlength, I personally can feel if the note is "on" pitch by a tactile difference in the vibration from when I intone the note a bit off.  

Now, I can't say that I know for sure if that is what they were trying to do with gut strings.   For all I know, gut strings may exhibit different effects if the afterlength is tuned or not.   But I did feel the effects were good enough on the acoustic violin I did them on that I felt it was well worth the day or so of fussing it had taken me to muddle through getting the afterlength in tune. 

Not so sure everyone would like the effect on electrics, though.  On my electric, the stronger vibrations actually caused some problems with parts of the (largely plastic) electric violin vibrating strongly enough to cause buzzing where the back and the internal cross-bracing touched or nearly touched.  I ended up having to pad some spots inside with craft foam and later a bit of silicone as a more permanent measure.   Then it started shaking some of the screws and nuts loose, so I ended up having to loc-tite those to stop that.  It also affected the sound in some ways that some people might not like.  On things like a strong bowed 5th on the open G and D strings, it kinda sounds a bit more like a pipe organ to me than any sort of stringed instrument I've ever heard. LOL 

That doesn't bother me so much, it is a good strong sound and very usable musically, but for some folks that want an electric violin to sound as much as possible like an acoustic violin, it may not be desirable.  I don't worry about it, and I kind of like unusual musical sounds, personally.  But I can't say that I am sure everyone would feel it was an improvement in electric violins, at least if they have one similar to mine. 

Now, so far as tailpieces, yeah, they certainly should also make some differences.  But I have only been messing with violins a few months now and haven't gotten to trying different tailpieces yet. 

@Fiddlestix:  Interesting!  330mm instead of the usually mentioned 327 or 328.. I wonder why? 

Fiddlestix said

 Also, if you have the old traditional fine tuner's on the tailpiece, that will affect the afterlength too, because the fine tuner's set more forward of the tailpiece, rather than the tuner's built into the tailpiece itself. Therefore the tailgut would have to be lengthened to get the proper length.

Yeah, now that would be logical, and makes perfect sense with the older style fine tuners.  But in reality, it is weirder than that.  I started by trying setting the tailgut so the place where the string leaves the ball end and would begin free vibration was at 55 mm.  And it ended up being way off.  After quite a bit of messing around I ended up with an actual string afterlength of something like 43mm. 

I think that at least that with that particular style of fine tuner, the metal of the tuner itself vibrates enough to be a part of the resonance picture.  Probably not a good part of the picture, if one is after the very best tone.  The other problem with them is they do actually change the string length enough when adjusted to fine tune the string that they can throw off the afterlength tuning anyway.  So with my electric (which has those), I mostly end up peg tuning anyway.  And yes, that does leave me wondering some days why I need fine tuners in the first place.  

With my Mendini acoustic, it had one of those black anodized alloy tailpieces with the build in fine tuners and it was much easier to get the afterlength set right.  It also didn't lose the afterlength tuning when the fine tuners were adjusted.  The Hoffmann has a similar type tailpiece, but made of carbon composite.  I haven't set the afterlength on that one yet.

I don't know as the built in tuners work the same with afterlength as no tuners or not.  Sometime I'll get ahold of a nice wood tailpiece as an upgrade for my violin and find out.  LOL