What I'm trying to say if you drill & slot a standard disc / rotor, there's chances that you may weaken its structure. In theory, its still serves the same purpose; cooling it.
The holes cool it & the slots are to de-glaze the brake pads. You know after hard braking, the pads' surface gets shiny & becomes like very smooth. So the slots sorta scrapes off that glazed layer to get a coarse surface to create more friction, hence more biting again.
Ready made branded cross drilled & slotted disc rotors different mar, factory made. They'd know how deep should the slots be & how many holes they can make to retain its structure intergrity as they've gone thru R&D.
So IMHO, it's not advisable to drill or slot a disc that was not specifically made for it. If you check your disc rotor, the inside, it's written "minimum thickness XX". If you've reached that minimum thickness, you'll have to replace it with a new rotor.
