Ruffy, a Special By-Law can be repealed using the same process that created it, that is by ≥75% of Owners present personally or by proxy voting in favour (to repeal) at a General Meeting.
That said, dogs simply don’t belong in apartments – it’s not fair to them or to the human residents who invariably have to tolerate barking that echos throughout the corridors every time the dog’s acute hearing detects a noise, and have to suffer those inconsiderate owners who allow their dogs to defecate on the Common Property because they’re too lazy or time-poor to take their animals to the dog park.
Sorry, but I don’t think you’re being reasonable by buying your apartment armed with the knowledge that the Special By-Law excluding dogs was in place, and by now even considering an approach to your Owners Corporation to repeal that Special By-Law simply for monetary gain.
As CBF suggested, perhaps you should reconsider your position by renting to a non-pet owning tenant.