The idea is simple. After making a suitable skill/stat check you can make your character appear more or less healthy. This way a character that might normally look spectacular can appear to be in excellent condition. Or the reverse.
This would be useful for combating meta assumptions and to allow a deeper disguise without having to use something like a poncho to hide that your character looks magnificent.
I would suggest that it be possible to move from one end of the spectrum to the other (unlike size changes which are limited to one step) but have each additional step require a more difficult check. This would allow characters who are masters of disguise with really good health descriptors appear merely excellent or the reverse.