Whitening an Old Yellow Skull?

I have a few mule deer bucks that I made into European mounts myself at home. I simmered them in sodium carbonate, picked them clean and then used peroxide to whiten. What I didn't know then was that I needed to degrease them to draw out the oils. Lo and behold, years later they have all yellowed.

My question is...can I degrease them now and whiten them again with any hopes of making them look better/whiter??

I have researched this topic online and have not found any good info about this - only information on how to it right the first time (which I did not)

Thanks!

Soak them in Acetone for a few weeks then try and whiten again. I like to use the bleaching powder mixed with 40 vol developer and make a paste. Crank up a couple shop lamps the old ones that produce heat and get that chemical reaction going. If you see smoke then its working.