Boiling plastic is not going to do anything for the color. The reason's it's yellow is because the fire retardant's in the plastic shed O2 atoms after their bonds have been weakened by exposure to UV light. Boiling it will do nothing to put oxygen back into the plastic. In order to restore the color, you need to get the plastic to rebond with oxygen. This is done with peroxide and oxy powder. A.K.A. retr0brite.

As far as restoring brittleness... I'd really have to see it to believe it. I can't see any plastic being restored by that unless it was right at the threshold of melting. But who wants to do that? You'd misshape the plastic. Parts would start to bulge and bend as it collapsed under it's own weight.