How can we place predefined texts from HTML elements? [on hold]

I'm a Product Manager and We build new feature as Personalized Email Campaigns.

we aim to prepare an easy to use Mail Campaign Edit Page within primitive customizable contents as Mail Subject , Mail Body title

We have some predefined Mail Subject and Mail Body title texts and that provides to make a decision quickly as a Customer

Mail Subject and Mail Body title must be selectable from a list. I demonstrated our UI and I attached it as below:

My question is about making a decision about showing predefined values with the best UI approach. Actually , We need alternative UI perspectives

We haven't any strict solution about placing predefined values within HTML elements from Campaign Edit Page.

Content lengths can be 200 characters and that is why we can't use any selectbox element; we must make a decision within the best approach and our main concern is that it's easy to use.

Could you please give us your suggestion about that?