ooh boy ooh boy, good (de)soldering is really NOT my thing especially PCB's.
But with some jumper cables I finally cracked the code ;)
IT'S WORKING !!
The LCD screen works, so for everybody trying this be aware of I2C address 0x27 or you need to hack/replace the firmware which nobody tried (mentioned) as far as I know.
Maybe I'll start a new topic "replacing the micro controller board" when I'm up to a new adventure.