First my query is if anyone has heard of this to even out skin tone whilst doing a frequency separation?
The idea is to use a two new blank layers between the high and low layers, you create a marquee on the top blank layer and fill it with white (you use this as a tool to see the issue). Move this white tool around over other problem areas that you can see.
On the very bottom blank layer (above the low layer) you do your retouching here.
The idea is with the White layer is to sample on this layer (where the tool is over the problem area), click the retouch layer below and use the healing brush (set to current and below) to retouch the image.
My second query is what are your desired ways of evening out skin tone?