Auto Oil changes.

Check owners manual see if other weight oil is recomended for say temp above 60 degs. As long as under warrenty would use what ois recomended. Why do you want to change?

I would only use the 5/20 the owner's manual recommends there is probably a reason why they want you to use the 5/20 probably because it has to be that thin to flow thru all the engine's orifices.

5-30 is fine as there is no way anyone can tell the difference anyway unless you tell them. I also like to use an additive called oil stabilizer like lucas brand. This ensures the oil is retained on engine parts while sitting instead of draining down to pan. Less chance of premature wear due to 'dry' starts.