There's no way of restoring alignment. Since it only affects the XP you get for artifacts it doesn't matter.

Alignment can not be changed later as far as I know. So if you plan to give the ultimate power to evil or neutral, be sure to do the maiden quest (the small island in the lower left corner of A4) first, as you need at least one good-aligned character for it.

For the mountains on the fire island, have you tried the spell "Etherealize"? I don't remember if that worked.

Are you sure you need at least one good character for the mermaid? I just dismissed my good characters before doing it and it worked as normal... It was the second shell I returned to her.

Tried etherialize and teleport for the mountains. Didn't work...

It's not difficult putting the maps you get from the wizard eye spell together. I guess they did it that way (or simply used the area map and replaced empty spots with the lava mountain symbol).

I meant the quest for the alicorn where you have to give love to the maid.
But now I remember, I think it was just necessary to have male characters (or at least one) and not good alignment.