(if you are using Steam cloud)
If you logout to main menu.
click game you wish to (backup) just move it to local
This will create a dated local backup. (i just used this (100%vanilla) Mist Updtd)
Then just move it back to the cloud ( the dated backup remains on local)

This can be done anytime ..
There is "save" in devcommands but i havent tested this yet in local mode only