Could someone please tell me how easy it would be to change an autumnal landscape so it resembles spring in Resolve? ie changing the colour of the trees and perhaps grass, while leaving other elements (tree trunks, sky, animals etc) untouched?
Lots of secondaries, lots of precise keying, some power windows, careful saturation, lots of experimentation... but a great deal of the approach depends on the nature of the original footage. There is no easy answer.
As one example of the opposite -- turning beautiful spring footage into brown, dreary fall -- check out Julius Friede's excellent work on "O Brother, Where Art Thou," which was done on the old daVinci 2K at Cinesite back in 2000. That work still holds up very well today.