Spring RTS Engine

[Foreword: I know absolutely nothing about anything.]
Would it be possible, given the source code, to add in 3rd or 1st person RPG mechanics? Or could I manage it given the features here (I gave the overview a thorough reading, and the feature list...a less...thorough one).

I want to ATTEMPT a hybrid game but I'd like to know if this engine is for me before I commit.

Yes, but you would be limited by spring maps with no buildings etc ..

Spring is not for you.