I know of a fairly unknown method to convert AIM accounts to AOL accounts. It involves a known limitation in how AOL authorizes new accounts and likely could be patched. Last time I tried this was about a year ago.
The good news is that AOL handles all inbound emails to "aim.com" and "aol.com" the same, so you can be comforted that people can email you. This is typically caused when an AOL account is canceled, and migrates out of their system and becomes an AIM account.
AOL staff can't change you back to "aol.com" at least no one there that can after their recent staff reductions.
Contact me privately and I might be able to attempt my method again.