For xlsm files you need to do an extra step at the start. Basically xlsm is a zipped format, so rename the extension to .zip and do the following:
- open and open the "xl" folder
- extract "vbaProject.bin"
- do hexedit method above on the "vbaProject.bin" file
- save the file and the reinsert into the zip
- rename back to xlsm.
- repeat steps previously outlined by changing and then removing the password.