Can .transformFluid add a function that can let it add/increase the amout of fluid? I also had a template.
.transformFluid(String increaseOrDecrease, String fluidName, int minAmount, @Optional Boolean reuse)
String increaseOrDecrease can let the amout of fluid increase or decrase.
This is depended on you. You can add it or turn it down.

Done in v1.11.2!
I split it into two different commands: .drainFluid to remove fluid, and .fillFluid to add fluid. More details on the wiki.

Thanks