if I make a mistake and post in the wrong communities, I can't change it, and I also have a hard time deleting it to correct my error.

we are living in Web 2.0 epoch, you know, so its no problem!
spending some extra life time on correcting the posts, yeah, that is a bit annoying -- but that isnt So Huge, right? just a minute or two.

and anyway that is not such a Big Mistake You Should Correct asap, haha

Much worse is when you double-post the same by error, or post something not appropriate / not suitable / directed to the totally wrong community... and you cant delete the post. then, indeed, you have to copy the post's content, erase it asap from the post, and add there something instead -- so that it was not empty and had something, sort of a filler xD

!BEER