An example would be the Python Grammar file. How do I apply your syntax highlighting on this file?

For example, executing the syntax highlight option via a command pallette option on a file?

According to specification, a comment in a BNF file starts with a semicolon (;) and extends to the end of the line.

This extension supports only line comments starting with # and block comments between (* and *). The latter is EBNF-style comment, the former is not copatible with neither BNF, EBNF or ABNF.

When using a comment in EBNF syntax in the line containing the equals sign, the comment is not highlighted as a comment:

here = does (* not work *);

but =
   here (* it works *);