You can't transfer a SPI flash image dump from one Mac to another, you will make a clone. Apple detects clones when you login at iCloud/iMessage/FaceTime and block both Macs - don't ever do it.
Editing the SPI flash image and changing the hardwareIDs (there are several) will only work if you correctly adjust the checksums (there are several and some are nested). While it's possible to do it, lot's of firmware knowledge is needed to do it successfully and it's totally out of reach of users.
MP6,1 don't have Firmware Programming Mode, so you will have to take it apart every time you adjust something and program it with an external programmer. Just this makes trial an error almost impossible.
Your best bet is to use BBS or go to Apple.