Can the subsidiary mortgage let the head office exercise its power?

Of course. The branch does not have independent legal person status, and belongs to the branches of the head office. To carry out business activities, you need to apply for authorization from the head office, but the branch office is qualified. The mortgage of a subsidiary can be exercised by the head office, because most of the activities of the branch are decided by the head office, so the branch has the right to exercise rights against the debtor on behalf of the head office.