I just started a few days ago so I won't be able to try for myself for a while. I just wanted to see if anyone had tried something like trying to send a message or temporarily "possess" yourself for a few minutes to do something like write out a message as proof that you were able to influence or at least contact yourself.

I wouldn't try to do change anything major yet beyond being able to see if it could be done. I would just visit myself from a few days ago and try to influence or at least contact this recent me to write out a simple message including putting the date visited and the date from when I do the astral projection and then tape the message to a wall. Since it would be time travel to just a few days ago I should be more receptive, expecting it to happen. Also it would not affect anyone else but still provide proof via the written message.

Even if initial attempts fail I think it could still be possible with more practice or skill in certain areas. I read that Robert Monroe visited a much younger version of himself and he remembered having that memory of being visited by himself when he was younger so conscious contact at least should be possible.