Can you convert a 135mm bicycle hub to 130mm?

Depends on the hub and your skills.

Sometimes there's an extra spacer on a 135 mm hub when compared to a 130 mm hub. If that is the case, this spacer can easily be removed - assuming you have the approropriate tools, usually a set of cone wrenches.

But sometimes there's one solid spacer only, in which case it'll have to be cut down or replaced, which'd be a bit harder.

In both cases above you'll end up with an axle that's a tad longer than before. If you use wheel nuts this isn't a problem, but if you use q/r skewersyou'll need to cut the axle down a bit or the skewers won't clamp the wheel in place properly.

And respacing the axle will also move the rim off-center so ideally the wheel should be re-dished to remain aligned in the frame.