Colin Pickard has an excellent answer, but there is one 'watch out' with this. There are instances (I haven't figured out the cause yet) where the total length of the "CMG=........GC=...." entry in the file is different from one excel file to the next. In some cases, this entry will be 137 bytes, and in others it will be 143 bytes. The 137 byte length is the odd one, and if this happens when you create your file with the '1234' password, just create another file, and it should jump to the 143 byte length.
I don't know if it is crucial, but I made sure I shut both the hex editor and excel down before reopening the file in Excel. I then had to go through the menus to open the VB Editor, into VBProject Properties and entered in the 'new' password to unlock the code. 2b1af7f3a8