Recommended Strings
 

so i just got a new Martin GPCPA4 Rosewood.... on the martin site it says Recommended Strings: Martin SP Lifespan Phosphor Bronze Light Gauge (MSP7100) ...if i go to a different brand/gauge is it bad for the nut on the guitar?

Not at all. Explore and find something you like, Martin and non-Martin alike. Of course Martin is going to promote their own brand of strings. ;-)

I use Wyres strings on my Martin and love them.

About the only thing on a small-bodied guitar is I'd stick with lights. Mediums might choke the sound and/or put too much tension on the top/neck.

Try some DR rare or sunbeams. They light up my OMCPA4. Their medium gauge is just fine for your Martin.

Hi Yoda,
On rosewood guitars, I give 80/20s a whirl. My favorite 80/20s are John Pearse.

Try lots of different strings over the next year or so. You will need to change them anyway and use is the only way of finding out what suits you and the guitar. As long as you don't put a MUCH heavier string on it you won't do any harm.
I'm another John Pearse enthusiast, been using them for quite a lot of years now. I use his "Slightly Light" in Phosphor Bronze.
MJRB

Those are all good recommendations, my Martin likes the DR Rares ....