expresses permission to do something. aishite mo ii = its ok to love tabete mo ii = its ok to eat (it) kaite mo ii = its ok to write etc.

Well, yes or no. That's the same particle as "also", but if used in "...te/de mo ii" pattern, it means "It is ok to..../with....". It implies that it's ok but not the first choice(compromise) or it's ok if you want(permission). "Kyou no bangohan wa tempra demo ii desu ka?" "Iidesu. Demo, udon no hoo ga sukidesu." (Is it ok for you to have tempra for today's dinner?--Yes, but I prefer udon better. )