Is it worth doing? That depends, a general member of public, possibly not, some one who is quite handy and can do the labour himself apart from the programing, possibly, some one in the trade who can get the parts, but has to pay for the labour, possibly, Me, I can normally get the parts cheapish (the cost can still mount up £££), I do all the labour myself and I get the programming done at trade price, I would only do this on my own MINI / MINIs (if anything should go wrong it's down to me & at my expense) due to saving the labour charge and only if I'm keeping the car for a while.
Should any warranty claims be refused, I can just do them myself anyway

, I think

.
I have just done a retrofit Climate Control on a MINI for the other ½, plus a few other little mods the same way

.
Can you call it an actual retrofit, I'm not sure, it depends on how you look at it

.
Would I do it for anyone else, No!, not unless they were a very good friend and it was at their own risk, plus I would have to check all the parts are working myself as I couldn't think of anything worse than doing all that and then it not work due to faulty parts

.