Can I change the Shooter Game to Third person buy using Blueprints only?

I believe that he means the shooter example in C++ from the marketplace, in which case the answer is yes, but not easily, as all of the PlayerCharacter class information resides in C++. You’d lose everything that makes the shooter a shooter. Try converting the First Person BP to a Third Person BP by migrating he 3rd person model to the First Person project, and set up the MyCharacter blueprint to use the 3rd person model.