No expert here, since we rarely ever use our RV A/C. But I'll throw in anyway.
No harm will be done if you restrict, or even close, any duct registers you choose. Within reason of course, but the vents on the bottom of the A/C itself should be plenty of flow by themselves.
Do you have the round registers, or rectangular. I haven't seen the round ones with flow restrictors, but there might be. The rectangular type usually do have them. But regardless of what type, you can easily restrict the flow. Just block some or all of the slots in the register. Use whatever type of tape that suits your décor preference.
If your goal is more even temperature throughout, the key is usually to push the air to the farthest ducts, and force it to flow back to the return at the main A/C. It's called Forced Air. Ideally the air flow should pass the thermostat location. And that is why they are most often placed in a hallway. So maybe you want to restrict the discharge on the bottom of the A/C unit, and open ducts in the bedroom.
I have experience with a new home and A/C where the bozos stuck the thermostat in a dead end of a hallway. No air flow. It must have been an easy place to pull the wires, because it was a stupid place for the stat. I moved it.