Normally, I would ask first in a comment but that seems to be a privilege not available to new users, so here goes:
Are you sure it was the radiator cap and not the overflow bottle? The radiator is usually full and getting 100ml in would be a struggle, not to mention that the green coolant would be staring you in the face. If you radiator wasn't full then you either have an empty overflow bottle, or your system wasn't burped properly the last time the coolant was changed, or you have a leaking head gasket introducing combustion gasses into your coolant system.
If it was the overflow bottle, there's a good chance that you car hasn't drawn the oil in from the overflow bottle yet. I say this because the pickup for the overflow bottle is near the bottom of the tank, engine oil floats on water and is insoluble in water.
My advice then is to remove the overflow bottle, clean it with a degreaser and refill with coolant. If you did actually get it in the radiator, let me know and I'll edit this answer.
As far as implications of oil in the radiator go: Oil will, in theory, attack the hoses and water pump seals. This would probably be a long term degradation rather than a sudden failure, and given the oil problem I doubt your engine will survive long enough to see the long term effects. My father's vehicle has been running with a slight oil-to-coolant leak for about two years, without any (visible) ill effects. The vast majority of the oil (after you've removed the head of oil floating in the radiator filler) will collect under the radiator cap as a creamy goo, which you can periodically remove.
Replacing the coolant wont do much to remove the oil that has coated the inner surfaces of your cooling system. If you have oil in the radiator and haven't run the car yet, siphon out the oil before it touches any more surfaces in the cooling system.