The Collaborative International Dictionary
Unprotestantize
Unprotestantize \Un*prot"es*tant*ize\, v. t. [1st pref. un- + protestantize.] To render other than Protestant; to cause to change from Protestantism to some other form of religion; to deprive of some Protestant feature or characteristic.
The attempt to unprotestantize the Church of England.
--Froude.
Wiktionary
unprotestantize
vb. (context transitive English) To cause to change from Protestantism to some other form of religion.