In a car, I'm quite comfortable making the switch between left and right, but best if it's in the 'right' sort of car. I.e. in a LHD car on the Continent, in a RHD car in the UK. In a few days I'm taking my own car (RHD naturally) to France and I know overtaking will be that little bit more awkward over there, but then I'm used to it.
I don't think there's any difference nowadays: some motorists from overseas (USA particularly) visiting UK, moan that they find it difficult to change gear with the left hand, but I reckon that's more to do with being used to automatics than anything else. Certainly I don't see any problem!
As for Samoa - what's happening there is pure lunacy IMHO! Let them go their own way if they wish - it's not a huge country and presumably not densely motorised, so perhaps they'll get away with it. See
here for the last time that a large country in the developed world (Sweden) made the switch - in 1967. According to the article it went smoothly but was a major upheaval and unpopular with the public.
Cycling - well that's different. I'm more likely to forget which side I should be on when cycling, since I don't have a steering wheel as a 'reference point' (my brakes are swapped over on the bike in France, that's all). And glancing behind over my left shoulder, instead of my right, doesn't come easy. I'm getting old... B)