I am currently in DEP so I can't offer any advice on specifics but I can give you my story.
You asked about changing your rating in DEP and it depends on how much you trust your recruiter. I found mine to be incredibly professional and responsible. I enlisted to the Navy while at away at college. There were no female slots open when I went to MEPs so I signed under the AECF job. In addition, my waivers (academic and a couple other ones) were still not officially cleared. A week later, I moved 500 miles back home with my parents. My recruiter “promised” to switch me to nuke the following month. Thankfully, he was a man of his word and I am now scheduled to ship June 2011.

However, I can tell you that I was a ball of nerves for a couple of weeks. The most important thing was that I REALLY wanted nuke but I could live being in the AECF job. It's completely up you but be ready to deal with the consequences. I'm sure there are plenty of horror stories involving promised jobs never given.
I have no idea what would happen if you got (or requested) a new recruiter.
On a side note, both my natural parents are immigrants. In fact, my birth father was deported for committing a felony. But keep in mind that waivers are looked on a case by case basis. (Info from my recruiter)