There are several limitations when using marker data to control generator parameters many of which are related to the order in which processes are evaluated internally. Improving this is on our wish list, but it's not likely to be included in RailClone 5. On the other hand, you can control some generators with markers if the generator is nested. The attached file (created in RC5 but probably works in earlier versions too) demonstrates this. Perhaps it can help with your situation.
Best,
Paul