ROM Hack Changing Picross rom's serial number from EU to USA

[nine0nine]

Currently, E1 / E2 and E3 are available ripped from the Europe eshop, where as E4 and E5 are from the USA shop.

I want to change the serial number the Euro releases of the Picross games to what I expect the USA releases are, in an attempt to unlock the extra puzzles in Picross E4 and E5 which are triggered when you boot the game and it sees you have already bought the previous games.

The extra games are unlocked in E3 by running E2, but nothing is unlocked in E4/5, so I can only assume its working via the games serial number ID.

So, I know its possible from reading the early .cia making tutorials, but to be honest they are a little over my head. Could someone give me a few pointers here on the easiest way to do this using the more recent rom tools?

Looking at the current releases below, it may just be a case of changing the E to a P.

1355 PICROSS e Jupiter Corporation

en,fr,de,it,es BigBlueBox 1024 CTR-JEXP
1335 PICROSS e2 Jupiter Corporation

en,fr,de,it,es BigBlueBox 1024 CTR-JP2P
1328 PICROSS e3 Jupiter Corporation

en,fr,de,it,es BigBlueBox 1024 CTR-JETP
1317 PICROSS e5 Jupiter Corporation

en,fr,es BigBlueBox 1024 CTR-KPQE
1207 Picross e4 Jupiter Corporation

en XPA 1024 CTR-JEPE