i don't have time for elaborate DIY but you need facelift BCM, gateway has to be 5Q0 high, MIB2 capable of ambiente light color (don't know which sw is capable, also I think that it can only control door rgb module not footwell ones, that can only mib2.5) or MIB2.5,
on rgb led housing: these housings have a longer protruding plastic for fiber optic which need to be cut, also sides needs to be cut to fit on old fiber optic;
pin1 – +12v Kl.30
pin2 – LIN-Bus
pin4 – -12v

You can use either passat or audi rgb housing
8W0 947 355 L
3G0 927 103 K
passat one comes with flat cable lenght around 10cm and connector while audi one connector goes directly to plastic housing no flat cable

for footwell rgb led housing use audi a4
8W0 947 415 A — front left
8W0 947 415 B — front right
8W0 947 415 С — rear left
8W0 947 415 D — rear right (didn't notice difference, didn't have time to look)
8K0 973 754

also there is for door card "pockets" smaller (square) housing rgb also
8W0 919 390 F
8W0 919 390 E
8K0 973 754