oil filter is pointless to change without an oil change and for that you need to be under the car and have taken the undertray off. So you might as well do the whole thing properly. Get a 32mm or similar spanner, too, it will make life easier.
I think (in fact, I'm pretty sure) that you MUST get under the car to change the airfilter, as the canister is screwed into place there.
Bret