If someone has an authority limit with two projects and I only have one of them, can I restore or revoke that authority assignment limit in Authority Manager?

Currently, this is not possible. You must have grantable authority that matches completely the limits on the other person's authority assignment. You cannot revoke or restore the authority assignment if you do not match. If it was revoked by someone else you can make a new authority grant for the one you have, but not for the other. If the authority needs to be revoked you will need to request someone with sufficient grantable authority to do it.