I like the names BUILD_VAR_POSITIONAL and BUILD_VAR_KEYWORD.

The downside is that this breaks relations between them and very similar opcodes BUILD_TUPLE_UNPACK and BUILD_MAP_UNPACK. The only differences between BUILD_*_UNPACK and BUILD_*_UNPACK_WITH_CALL opcodes is that the latter takes a function name from the stack for error message and BUILD_MAP_UNPACK_WITH_CALL doesn't allow key duplications in contrary to BUILD_MAP_UNPACK. But the names BUILD_TUPLE_UNPACK and BUILD_MAP_UNPACK doesn't look very good too.