Hi Andy,
I have been following your mod and I have followed your guide and instructions to the lists. I too am in the UK and having the same issue as you originally. I have installed the new switch pack, made all the changes in Forscan. However it will not let me change the Cruise Control setting in the PCM. By this I mean, I can change the option, but when it writes, it fails and says it was interrupted. I've tested the vehicle and ACC does work, but it has the same fault you had that once it brakes once, it goes unavailable. I've shed the DTC's and it shows incorrect message from PCM to CCM. I can only assume that until I can find a way to get the PCM written, it will not work.
Did you encounter any PCM writing issues on Forscan? is there another tool to use like FOCCUS maybe? Any suggestions would be really good please.