Is it possible to rename the wp-admin folder?
I know I could just rename it, but unless it’s supported by the code lots of things would break.
If I use a custom folder name, it will make it slightly more secure, security by obscurity and all that.
Unfortunately it’s not currently possible nor does there appear to be will to consider it as a modification as you can see by this recent thread on the wp-hackers list and this ticket on trac.
If you’d really like to see this be revisited I’d suggest:
Present your case on wp-hackers but be forewarned your use-case better be good and not “security through obscurity” or it will get shot down as above.
Present your argument in a trac ticket with the same caveats.
Even better, upload a patch to trac that enables your desired functionality. It’s much harder to say no when the work has already been done (but of course, they do have a preference for saying “no” a lot more often than they say “yes” so be forewarned.)