In reply to rcollins:
Partly depends what sort of changes you want to research ! - it's a potentially huge topic: technical changes, social changes, club development, transport, huts, rescue, etc.
As well as all the good suggestions above, W.H.Murray's 'Scotland's Mountains' (SMC 1987) has a succinct but useful historical chapter, 'The Development of Mountaineering', with about ten pages covering the years from 1930 to 1960, so that would be a good start. Dr Ken Crocket, who published his monumental 'Mountaineering in Scotland: the early years' for the SMC last year, is now working on his volume 2, which will carry that forward from the end of WWI to the arrival of front-pointing, c.1970. You could also approach the SMC's Archivist and their Image Custodian (see the SMC website for contacts). But as voluntary officers I'm sure they'll prefer it if you can give them quite specific questions rather than this very general one, so better to do the background reading first.