AFAIK there are at least two manufacturers that offers conversion kist from ABC to conventional struts. Arnott and Strutmasters. I read some comments regarding one conversion made by a guy in the US. He decided to add swaybars to his CL after having installed the conventional strut replacement kit. Strutmasters offers one kit for $ 1319. "Easy to install" they advertise...
I once owned a CL500 but never experienced any problems with the ABC-system. BUT: It is absolutely vital for the life span of that system to replace the ABC oil and filter at regular intervals. For the M/Y 00 that I owned, there was no oil change interval specified and 6 years old, the oil in the system was greysh and smelly. (Fresh oil is transparent/green). I had a replacement in mind should the system in my CL fail but after 160,000 when I sold the CL km the system was still performing well w/o any issues.
I doubt that neither Arnott or Strutmasters would sell their systems without offering/including some technology that turns any warning light off. What MOT i the UK has to say about it I cannot say. At least in the US these kits seems to be perfectly legal for use on public roads.
What I have not checked is how to deal with the coaxial pump that handles both the steering and the ABC-system in an unmodified car.