XF 2.2 How to apply a template modification manually as opposed to enabling automatically apply template modification checkbox

[Earl]

I have a whole new template for the contact us page (misc/contact). I want the template modification to be applied only to guests.
I tried messing up with <xf:if is="!$xf.visitor.user_id"> template syntax but when new xenforo updates comes, the pattern got broken few times.

I just wanna know how to apply a template modification manually.

So I can simply do a find and replacement using regex /.((.|\n))/ and replace a whole new template then apply the modification only for users.

 

[Earl]

okay, I found another way to solve my problem.
I extended the Misc class actionContact and changed the template name to a different template name and created that template manually instead of using the template modification system.

But I'd love to know how you apply template modifications manually.