The discus may not be hybrids, rather just selectively bred lines. This is a good reason for using Latin names instead of common names. If you took a batch of Symphysodon discus fry and selectively bred two different looks for several generations, they will still both be Symphysodon discus unless you interbreed them with another species. For example, you could call them Symphysodon discus 'Stripey' and Symphysodon discus 'Plain'. If you crossed a 'Plain' with a 'Stripey' the fry would still be Symphysodon discus, in the same way that if an Asian and European person have a child it is still Homo sapiens. All the different colour strains of asian arowana are still Scleropages formosus.
But getting back to the original question, you could hybridise cories, but one would have to ask why? You could possibly do it to satisfy your own curiosity, but unless you came up with something very worth-while (ie with some quality far superior to any individual species) I would suggest keeping the hybrids to yourself. As Ryan suggested, diluting species is something we should try to avoid if MAF are considering further restrictions on the border. If one of your hybrids looked a lot like C. sterbai an unsuspecting person may breed it to their C. sterbai and then on-sell the fry as C. sterbai not knowing they aren't true.