SELF TRIM / POKE / PLUG

 
SELF TRIM
When positioning the new geometry against an intricate surface, for a perfect fit use the "Self Trim" option.
selftrim
POKE / PLUG

In order the have the "carving shape" also turned into a mesh object (while also carving the base object ) you can turn on "Poke".

This will simultaneously perform a "Remove"(Difference) and "Add"(Union) operation, keeping the hole and the carving shape.
poke
The difference between Poke and Plug is, with Plug the new object is trimmed flush to the surface.

poke

Poke

plug

Plug
Self Trim & Poke Tools
selftrim