Technically applying film or spray tinting means they do not conform any more (but may still pass Mot). Commercially available smoked/tinted lights should be OK.
One of the issues with tinting is built in reflective strip may no longer work or show red so additional reflector should be added (which looks gash so people don't apply them)
Having tinted lights on many previous vehicles I chose not to on my T6 as I do a lot of mileage and the insurance implications of being rear ended and claiming being unable to see brake/turn signals concerned me.