Colin, I haven't done this for a while, and I am no technie, but in essence:
Install a hex editor such as the example i stated. Twocows.com is a good link to access free software - and this is where I got mine.
Start the Hex editor and select open new file (or such like), and open one of the memory map files that has suffix .qct.
The file will open, scroll to the very end, and the last part of the text on thr right will read "2001crowncopyright".
Change "2001" to "2005" and then file/save as a new file with the same name but in a new folder.
Now you can open this map from V5 of Memory Map - probably!
p.s. don't blame me if this doesn't work. Make sure you save a copy of the original .qct before you change anything.