Joined: Jul 2015
Posts: 7,498
Likes: 3,301
From: NW Oregon
Bikes: 1982 Trek 930R Custom, '91 Diamondback Ascent w/ XT, XTR updates, Fuji Team Pro CF road flyer, Specialized Sirrus Gravel Convert, '09 Comencal Meta 5.5 XC, '02 Marin MBX500, '84 Gitane Criterium bike
if the shop/mechanic complains about, or refuses to put on parts you provide, find another shop. That amounts to being childish, and whining about them not getting to make more profit off of you.
that said,,, 105 and ultegra cassettes of the same gear and tooth count should swap with virtually no change to the fine tuning of the rear derailleur.