Is it "wise" to replace the McSpad friction tuners with Whittner pegs? Probably. There are other "planetary tuners which look more traditional -- Perfection and Knilling. Geared pegs will not affect how the instrument sounds.
One thing to know is that the McSpadden tuning shaft holes are parallel, not tapered, and the Whittner pegs are tapered. For proper fit and function you should reame the holes with a standard 1:30 tapered instrument reamer.
The Whittner website WITTNER® - Finetune-Pegs, Made in Germany (wittner-gmbh.de) gives you the necessary tech specs for each of their models. At a glance it appears that their models for 4/4 and 3/4 violins are the size you'll want. Similar information is available for Perfection and Knilling planetary tuners of course.
updated by @ken-hulme: 07/08/21 06:11:59PM