The point would be that he could touch the woman he loves. Their True Love wouldn't burn him, apparently, if he turned his Hunger to feeding on something other than lust.
It is a debate that has been on these boards for years, and frankly never made much sense to me.
That is, sex with another however casual or even supposedly rape cancels the true love protection. Thomas and Justine are just as much in love as they ever were, but because she had sex with that woman and Thomas feeds on another[sex] the protection is kaput.. Which up until she found herself pregnant and the embryo Hunger inside her embryo child began to feed off of her Justine was perfectly fine with, as was Thomas. Which is all ironic in the first place, because both were unfaithful so they could physically express the true love they have for one another without Thomas becoming a french fry..
Now, arguably, if he changed to something else he wouldn't accidentally feed on Justine via touch, but I don't know if that would work... I don't think he'd lose the ability to feed on lust, and Thomas says his Hunger is specifically attracted to Justine (he can touch other people with True Love protection without being burned, after all...)
No, he cannot as I understand it. He cannot touch anyone with True Love protection. However real True Love is rare I think. It must have been awkward in the beauty parlor if one of his clients was protected by True Love, then a pair of gloves was in order and the lady benefited from his hair dressing skills.