Yes I will have a play around with rules. Don’t have ready access to mess about with live hardware, so will take a while, but no hurry I guess.
I like the enable/disable option actually - with the wide variety of possible Modbus devices it may have more uses than just error management.
Maybe implement as variable poll rate - set a binding master poll period, then set individual slave rates as fractions - zero effectively disabled, 1 for standard polling (default), 2 for half rate, 10 for one-tenth rate etc.