At the end the of the day your saddle is your saddle and can do whatever you want to your saddle even before the warranty runs out...but don't expect Brooks to cover your saddle if you screw it up using neets oil or water or motor oil or whatever that was not specifically outlined in the care instructions.
I've said this before so I'll bore you with it again; Brooks has been making saddles for over 100 years and they know exactly how to get the longest life possible out of their saddles, all the owner has to do is follow those directions. Don't take my word for it, I'm like you just another forum member, but rather take Brooks word for it. You can either read the care and warranty info that came with your saddle, or you can go to their web site where they spell out the care and warranty info, or you can e-mail them with any questions about using other products on their saddles and see what they say.