Many thanks for your answer Alfred, I did more or less the same with my GO 910, but soldering wasn't necessary, just only a gap in the body was needed.
I know it's not possible with every One, I've an old One too, with PB as the first two characters, TomTom tell me TomTom ONE 125 with just only 1GB
As far as I know, nobody succeeded yet to modify this model ?