Yosemite upgrade: protecting what I have now...

Because I boot from an SSD and I couldn’t stand running out of room every two minutes, I moved my user folder to a separate internal drive in my Mac Pro. (Yes, it can be done - I forget the precise steps, but I do recall that it was accomplished within the Accounts preference, no terminal needed…)

I want to upgrade to Yosemite, but I’ve personally seen and heard of enough issues that I want to make sure that I can UNDO it painlessly. Using Carbon Copy Cloner to make an exact clone of my SSD is step One to having an immediate reversal option, but is there anything in my user folder that could get Yosemit-fied? I don’t want to clone the whole thing, because it’s huge, I’m just concerned with files that a newly installed system might immediately mess with that would screw me up.

Anyone know?

Yosemite will not touch anything in /Users (to the best of my knowledge).