I wouldn't expect the 35mm adapters I've seen to damage a camera -- they're just spool ends to center a 135 cassette and provide compatible drive for use in a 120 camera. I've now got three sets of those -- two pair of 35mm only that I use in the 220 back on my RB67, and a set that includes an adapted takeup spool to ensure centered takeup (came with my new pinhole camera).
There are/were 35mm adapters for some medium format cameras that included a frame mask, cover for the ruby window, and some means to correct or manage the frame spacing. Yashica 635, for instance, was a 6x6 TLR that had a 35mm adapter (when new).