First a general comment, you should be doing your formatting using Styles. I don't mean the checkbox in the content control properties, I mean in general. You are using direct formatting for your font. Understanding Styles in Microsoft Word
Not using styles will make your template and documents produced from it harder to edit.

As to your problem: Try using the protection method intended for content controls: Restrict Editing: No Changes (with exceptions). See attached.

Attached Files

test_template 2.dotx (22.7 KB, 13 views)