I'm thinking about ordering a custom-made Framus guitar, but the prices go quickly up when you start to do modifications.
I was thinking about substituting the stock Framus locking machine heads/tuners with backlocking Schaller ones.

Could a different brand of locking machine heads produce more/less stable tuning, or is it all just the same - with only different cosmetic/practical issues?

The schallers are still pretty decent tuners. Only ones to stay away from are the no-namers on cheap guitars.
5150 combo
GSP1101 + Tech 21 PE60

ESP LTD M-255 w/ SD Full Shred
Kramer Vanguard w/ JE-1000 active preamp
Douglas WF-150sn w/ GFS "Hot Lead" set

Bos SD-1 (boost)

My Youtube Vids http://youtube.com/user/mogar
Schallers, Sperzels and Gotoh are a few of what i know are good brands.
Ibanez RG321MH (Air Classic/Tone Zone)
Fernandes Telecaster (Twang King/stock bridge pickup)
Blackstar HT-20 (Scumback 55 speaker/ Tung Sol tubes)
TC Electronic Nova Repeater
Lava Cables Clear Connect, Soar and Mini ELC