GNU frontend modification

Hi All, Greetings for the day !! I am trying to modify the GNU Pascal fronted. I have gone through GNU Pascal manual and GNU Pascal internals site and this is what I have understood. 1.Lexer - I need to modify pascal-lex.l file and using flex compile it to lex.yy.c file.Rename this file to pascal-lex.c 2. Parser - I need to modify parse.y file and using bison compile it to parse.c file. Now what I am supposed to do next, to make these changes reflect when I compile a pascal file ? Thanks a lot in advance. Thanks and regards, Rajat