I have a PCB with a BGA component, when I order the stencil, I don't want the stencil to have cutouts for these pads.

I've read that you can select the pad/s and set a negative value for the Paste Mask Expansion. For the particular component model I am using (the STM32H747AII6) - it turns out the Paste Mask Expansion is already set to -100mm. 

For another component on the board (the central tiny BGA) - this actually works, but for some reason, it doesn't work with the STM32H747AII6.