Engraving a Rolex... does it lose value?

[ncamatagua]

Hi, I'm new to the forum, don't have a Rolex but convinced myself of getting a GMT-Master II.
I want to get it to reward myself for professional success, and since I have two science degrees and no graduation ring, I thought it'd be nice to engrave it with my name, and degree dates.

After reading a lot on this forum, I'm wary of internet dealers, so my intention is to buy it from an AD.

Questions:
Will the AD be able to do a neat engraving? (as in does he have the machines?)
Will the watch lose value cause is engraved?

Thanks for your expert opinion.

Cheers
NC