Can you command deities and have them posses you so you can receive their power.
Short answer: Yes, though command is probably not the word to use. It’s a good way to get slapped down by them. Ask with authority and respect.
I agree with DarkestKnight. You have to respect gods as equals. In fact try to respect spirits in general.
You can invoke gods and become temporarily merged with them, I wouldn’t say its the same thing as a possession. The more you connect to them the more you literally become them.
Not command.Request. Otherwise sure.
Ea Koetting teaches in one of his courses to force the power from an entity he gives various beings that you take the power from some give it, but some must be forced.