Yes, everything can be done and it's usually the last 10-20% of the work, though some members are still just saving the beauty output and play around with some filters.
I just wanted to point them subtly, into that direction, so that they see that composited image gives one much more control over the final output.
Need 4% more or less SSS strength? Don't need to render all those frames again, especially if the client later decides it to have a different hue etc.