I have a questions

playing in franchise mode can I download a current roster patch and use it to change the roster Iam using in the franchise??? I hope you guys understand my question.

Unfortunately not. You can't apply a roster update to a Franchise already in progress.

you sort of can....
but all the trades, stats, and things would be gone
there would probably be other glitches too

so it's better not to

If you want to put in rookies, check out the "Sticky: heres how to put rookies in draft after franchise is started" forum.