What are my chances of submitting a 4187 and having it go through after recently picking up my E-5?

If you reenlisted for Germany you can easily cancel your assignment. But your branch isn't going to want to put you into Recruiting until you've had at least one year of rated time

Just picking up SGT and now want to do Recruiting? Chances are slim that you would get picked up. But, no harm in trying. Worse case is they say no to your packet and you go to Germany.

Officially you need to be an E5 for a year before you can come over to recruiting. but it just depends on if branch selects you. But then your DA select instead of volunteering.