Would love to see the ability to utilize expense and extra categories in my formulas

Would love to see the ability to utilize expense and extra categories in my formulas.

I have run into a situation as a property manager where I am needing to refund my client for a mistake made. I would love to be able to specific a category that I can subtract from my payout that can be used in the formulas. Most of the time it will be 0, but if I need it, it will subtract from my fee and give it to the owner.