No problem to use.
The 40 just means your better at higher temps like above 95°F.
AND if your in a hot location, 10w-40 would be the weight to use.
Well now.. Larger number doesn't automatically = better.
Better against heat, sure, but at no cost for the engine or drawback..?
Bigger number indicates that the oil has more viscosity, aka thicker.
And just for the record, the 10w-40 oil might be just fine for the Rebel, seeing as 10 more isn't a massive jump.
However; That doens't mean that this can't cause some issues in an engine.
And I'm just speaking in general here now, it's not directly tied to just the Rebel here.
But some engines can be made with some rather small and narrow passages for the oil to flow through, and as such is strictly meant for a lower viscosity oil for it to function fully.
So even changing the oil to a 10w-40 over the standard 10w-30 it's meant to have can have unwanted results.
Just something to think about and be aware of, so that people doesn't go on thinking that bigger number is better no matter what.