Is it possible?
Yes. how would I do that?
There are two ways:a) Use a compiler.
b) Use an interpreter (scripting).
By far the least technical of the two would be to use some form of scripting. Many commercial FPS engines (Unreal and Source for example) use a scripting language like Lua or Python as the interface between the game itself, and the underlying engine.
Since BlitzMAX already has built-in Lua support, there's no prize for guessing which scripting language I think would be most sensible.