Yea but mate. You wouldn't need to swap out the oil in between services. You would be totally fine going on cbs. I see what your saying you want to know wether its totally worth it or for the extra cost.
Lets say its not. ... Your friend will still change very frequently. Especially when its free. I am not sure about the whole changing oil in the dark thing, but then again I have no knowledge of uv exposure.
So did you manage to get the oil out for a sample?