if i want to move all the content of the oblivion directory to another place, the game still will work? Or I have to uninstall everything and re-install all?

the thing is:
C:/Games/Oblivion -> C:/Games/Bethesda/Oblivion

I don't have oblivion for PC, but i've screwed around with other games directories before and they were fine.
If you really wanted to be sure, then yeah i guess you could just re-install it.

Do a re-installation. It's much safer than all the registry edits you'd have to make doing it manually.