If I change the project folder name and the ?????.agk (and ????.layout and ?????.cbp?) to the same name... have I changed the project name (and will all work OK) or is there more to it?

That's what i have always done.
Note that you can edit the .agk file (and i imagine the other files as well)

Thanks blink0k - cool... time to rename the project! When I started a few years back I just called it "platform game"....