Haven't noticed any mention of this anywhere else, but I got bitten by this rather badly, and thought I'd better bring it up here…

If you have a local variable in some sprite, and other sprites also have a local by the same name, then changing the name in the first sprite will change all uses of local variables of the same name within the scripts of other sprites (“set” & “change” blocks, and anywhere it's used in expressions, etc.).

In fact, if you rename to a variable name that another sprite already has, you can really mess up your project quite badly. It can lead to some pretty nasty problems that take considerable time to sort out…

Local variables in scripts of other sprites shouldn't change when renaming, only global vars should change everywhere.
(Hoping it's not too hard to fix this…)