Installing K&K Pure Western or Fishman Thinline passive only calls for reaming the endpin hole slightly larger to fit the input jack which also becomes the strap holder or endpin.
I have K&K's in a D-15 and an OM16GT.
I have a Thinline in a Martin 12 string.
I have the K&K Pure Preamp that I clip to my belt or amp. There are no dials or slide-fades on the guitars.
A good luthier can remove the endpin electronic jack and match the mahogany or rosewood and plug the end pin hole back to normal size some day. They glue in a tiny wooden dough-nut.
Pay a luthier to do the install. It's cheap ($35). Do not ream the end pin hole on a Martin by yourself.
K&K Pure Westerns are fantastic......about $135 installed.
http://www.kksound.com/purewestern.html
If you are playing acoustic guitar (unamplified) in a small group of people...they cannot even see or tell that the guitar has electronics.