I have used NEI Mold Prep sparingly in the cavities. It can help with a new mold, and it wears off slowly. By the time it wears off the mold is broken in and no longer needs it. Any change in diameter is not noticeable.
Avoid spray-on mold release compounds. They work by reducing fill-out, you get smaller bullets. They build up on the mold faces, you have a double layer there, you get out-of-round bullets. They fill in the vent lines. Yes, release was improved, the bad bullets fell right out! One spray-on was very difficult to remove.
The instructions with new LEE molds are specific:
"DO NOT USE DROP OUT MOLD RELEASE SPRAY."