How to replace a file in a msi installer?

Try InstEd - an installer editor at http://www.instedit.com/. It has a 30 day trial, and it works for me. You extract the files to a folder, edit, rebuild the cab, and then save the MSI. Everything but the edit of your files is done in the GUI.

Not a great program but I paid my $30 to be able to quickly edit files in the MSI.

I don't work for InstEd or related in any way other than paying for and using the application.