aekhong,
Great thanks to create this page of tutorial. I saw a thread from other forum, (believe u know which one, let me know if u are not, i will PM you) It seem that SiamMarine mentioned there is possible to convert back to US. I am beginner on this GPS firmwave, appreciate if you could help to understand thier explanation ?
"@AussieDJM
Yes, you can always come back to US firmware with gupdate.gcd(US) because it has the same boot.bin(us)
More information...
This picture is rgn for 7x5 series US(Whatever HWID) --> Sg/Mal (HWID 1069)
After flashing rgn ,Nuvi will have boot.bim HWID 1069(Sg/Mal) instead 870(US).
So it need modified rgn to come back to US., and just simply upgrade to higher or lower Sg/Mal firmware by using Sg/Mal gupdate.gcd."