I’ve always been leary about doing anything that changes the mass of the top, or that messes with the mechanical coupling between the strings and the guitar. We make a big deal about saddle material, about getting the best possible seating of the saddle in the slot to maximize conduction, and then put a piezo element between that saddle and the bridge. And drilling the top and then weighting it with knobs and things, or with pickups (particularly in the lower bout), will, i believe, change the sound of the guitar - mostly by stealing some of the high frequency components.
The sound-hole pickup is least obtrusive in this respect, since it’s all the way up by a part of the top that doesn’t vibrate much anyway. But even these, by reducing the size of the sound hole, will change the Helmholtz resonance of the guitar - probably not a show-stopper, but still - it will sound different.
I once had to repair the top of a mid-‘70s Aria guitar, as the bridge had pulled up and taken some of the top with it. This guitar had been made without a bridge plate, which may have contributed to why it sounded so much better than its price would have indicated. I had to make a bridgeplate and glue it in. The guitar still sounds OK, but nothing like it did before this happened.
I think a well-designed and built acoustic-electric would be ok, since the mass of the electronics and pickups is (I hope) designed in and accounted for. But any aftermarket mods will probably change the unplugged sound of the guitar.
A lot of words to say, yeah - an external microphone is the most faithful way to amplify or record acoustic guitar, though you probably have some feedback issues to deal with...
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