If I am active duty Navy now, can I switch and become a part of a different branch as a Reservist or National Guardsman?

At the end of your contract, sure. Before then, not very likely.

Absolutely. I was prior AF, and eventually went back in as a reservist on flying status, and there were prior service members from all branches in my unit, except maybe the USCG, but there just aren't as many of them.

Depending on your RE code and discharge you should have no problem switching to Army Reserve or National Guard after ETS. You would most likely keep the same rank but would have to go to Army Basic and MOS training (AIT). Sometimes prior service Navy gets to go to a short course called Minuteman training in lieu of Basic. Best of luck!

I went into the DEP program a few years ago, and decided to go guard instead. I just got a "refusal to enlist" from the navy which the guard happily overlooked. That oath you take at MEPS when you DEP in is more ceremonial than anything. Your contract doesnt start till your ship date. However, that time in the DEP does count towards your inactive ready reserves time. If you enlisted into the guard, you contract starts right then and there. If you have 3 months until basic, thats 3 months already done with your contract. You get paid for your drill weekends as well.