Ive got 2 rings equipped with constant effects and some more enchanted in backpack (like levitate and open - spells that i need time after time). But whenever i use this enchanted ring via hotkey they are equipped instead iof the ones with constant effect. Any way to prevent this?

No.
But I do believe Hrnchamd mentioned about how he's investigating if he can fix that (with the MW Code Patch)

I may be confused, but rings and other enchanted items must be equipped in order for them to be used at all. I do not see a problem.

Well, logically I would assume that most items need not be worn when using their "on use" powers. I mean, it's hard to imagine someone launching a magical projectile from an amulet worn around their necks, or from their left pauldron for that matter. But yes, in Morrowind you need to wear/wield items in order to use their power with the exception of spell scrolls.

Well, I've never seen or read or played a fantasy story where effects on worn items of any kind could be activated without wearing them first. Seems pretty normal to me.