Appointed is usually followed by the preposition 'as'. E.g. Mr. X has been appointed as the Principal of ABC College. However, if you want to use the preposition 'to' in the sentence, you will have to add, 'to the post' in addition.
English Language Learners Definition of appoint : to choose (someone) to have a particular job : to give (someone) a position or duty. : to decide or establish... more