That could be an interesting approach, i would not hope for much though. Such people exist, but they mostly perform standard functions such as odometer changes like you mentioned and immo services. There might be someone who can go beyond the standard stuff but i'd be looking for a needle in the haystack most likely.
I reckon Eddie-NLs suggestion is the most sensible solution in case i need the extra functionality of the FIS. Making the boost gauge work in the GTI cluster would be a cool mod, that was the main reason of going for it. The information i'd get from it might be even less important than the coolant temperature (less boring though). The stock boost gauge doesn't show absolute numbers of pressure rather than a % of max pressure. And max pressure fluctuates in the twincharged engines. So it's more like a health monitor if anything.
Anyway, i've seen a modified cluster somewhere sometime, but i'm suspecting that the guy just used the clocks and front fascia from the GTI cluster but kept the PCBs from the GT cluster, which would mean wrong speedometer scaling, nothing extreme though. But i don't feel comfortable with that so i'll leave things be for now.
