Can I switch between Apple ID and Email login?

Yes.

To switch from Apple ID to Email & Password, sign into Glass for Web. On your profile page, go to Settings > Account. From there, you'll be able to unlink your Apple ID and set your Email & Password.

To switch your membership from an Apple subscription to a credit card is a little more complicated. You'll need to cancel the subscription on Apple under Settings > Apple ID > Subscriptions. Once it runs out, you can restart your membership on Web. (Don't worry, your Glass account is safe during the lapse in membership.)