(1) Some of the site gurus may be able to help here. I think the short answer is no, the search engine on MARP doesn't currently do this. An indirect way is to run MAME with a command like(posted 9370 days ago)mame -listclones galaga
to get your clones listing and hand enter them on the MARP search page.
(2) I think you need to ask server to 'expire your cookies'. When you submit a board item look for a line at the bottom of your browser that says
Note: if the default name/email above aren't correct, you can ask this server to expire your cookies.