making a new enitiy?

OK so, its bothered me that maps involving one flag or bringing the flag to the enemy base is a simple briefcase. I came up with the idea to change that and maybe make the intelligence something a little more threatening.

So I found, the fgd and im pretty sure Ive found what I need to copy paste and change things for the flag.

BUT before I do this, I realize that even if I create this new entity I want to make sure I can do this without any problems and not waste my time.

My question is, is it possible to pakrat an fgd so it can be used when entering a map? Or is this just not going to work?

alright thanks for the info. servers are way over my head