So let's say I was going to make a comic that originally complied with the M rating but turned into an A, would I be able to still access it? I'm not quite 18 and and wouldn't feel comfortable creating a new account (and I know you're not meant to :P).
I could always host it somewhere else with a more lax view of things and move over here in a few months if necessary but that's if I actually get this theoretical comic going first. Are there any good examples of what people can get away with using an M rating?

You can have nutidy, etc with an M rating, but the A rating is reserved for sexualized nudity and the sex act, for the most part. It depends on how it's depicted. Two people under a bedsheet having sex would be M, as it's more discreet than the same image without the bedsheet (visible genitals or no). It would depend on the language too. If there was a whole lot of dirty-talkin' and stuff (basically the sex would be in the words), even with the bedsheet, it would probably qualify technically as A.

I'm not sure about the answer to your question about being able to access your own A-rated comic if you are under 18... I'd hope someone could do that, but I'm not sure if the programming has taken that into account.

Also, it's ok to make a second account. People can have as many accounts and as many comics as they like. What we don't like is when people use those secondary accounts to harrass other users, screw around on the forums, etc. Those kinds of things aren't okay anyway, but most often when we see it, it's someone using a secondary account because they know they'll get in trouble for it and don't want to risk their primary account. (What some of them don't know is that we know who they are :))