is this possible?

I would like to create a spell in a hero arena type map where the one player completely takes control of another player for a few secs after which control is given back.

Can this be done?

What about team switching, can a player be switched from one team to another for a limited time? That would be a cheaper version of the above but still effective.

Instead of switching players, why dont you just do a big for loop that will loop through each of the possessed players units and gives them to the other player for a limited amount of time. Better put them in an array for some time so you can unconvert them when the time comes.

Can you do this for heroes or just regular units?

What action "gives" the unit to the other player?

Change ownership of Unit(most likely will need a variable if players choose their heroes.) to Player and Change(or retain, you can choose this to) color.

That's in the unit category.

Isn't it possible with Charm? Just give Charm a duration. Or maybe that spell of Mal'Ganis.