When you want to use the template with a character, you could go to “add new” - add feature or content pack - add the third person template - open the world settings - apply the gamemode from the template to to the gamemode slot 
When you want to use the template with a character, you could go to “add new” - add feature or content pack - add the third person template - open the world settings - apply the gamemode from the template to to the gamemode slot