Yes you can efile it. Don't know about PA.

That's an after April 15 project in my book.

How much changed? Sometimes I'll tell the client I'll have to charge you more than it's worth to amend the return. If they send you a bill for $xx, pay it. Or if it would be a small refund, tough cookies.

EDIT: I read too fast. Now I see you said it is a new account, not a corrected 1099.