unprotestantize

from The Century Dictionary.

• To cause to change from the Protestant religion to some other; render other than Protestant; divest of Protestant characteristics or features.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb transitive To cause to change from Protestantism to some other form of religion.