Never tried myself, but in a recent game the UP council slapped a "no further tech trading" resolution over me when I was still weak

I actually think it's cool that you can run into it, but IMO what would be even better is if you could bring this (or other resolutions) to the table again later, provided you are the UP chair.

Do we have once agreed UP stuff for all eternity or is there a way to change it later, when your civ has the UP chair?

If not IMO it would be a nice thing to have, having this set once for the whole game seems a bit rigid, and also "unrealistic" (given that political approaches, various sides' political weight, or the whole make-up of intl orgs etc. are not static, they always change over longer periods of time).