Belt Tensioner Bearing Replacement
 

Is there a DIY link somewhere? Is it a simple process of putting a socket on the nut for removal? I think I can figure how to press the old bearing out of the pulley and pressing the new one in. Thanks!

Yes, it's just removing the bolt - but I wouldn't replace just the bearing. Get the complete tensioner roller assembly. I replaced my bearing in the old roller but it only lasted +/- 10,000 km before the bearing started to rattle....
The nut is actually a bolt which needs to be torqued correctly.

I can't seem to find any torque spec for the tensioner bolt in my Bentley manual. I would really hate to guess. Anyone know?

It is all in Search.
Short version : yes you can press out the bearing from the pulley with the correc equipment and replace with generic.
The pulley will probably crack unless you are an expert.
Suggest you check Rock Auto for the complete pulley+ bearing to avoid issues and get a new Gates belt while you are there ?
Be very careful checking the alignment of the pullies. Use a steel straightedge across the face of all adjacent faces. If they are misaligned - eve slightly ,you'll have issues....