I use a number of custom sensors being served via the Advanced XML EXE sensor. I have tried passing the warning and error limits in the XML but this only applies to sensor creation. I would love to be able to set the values dynamically based on certain circumstances determined by the code. I release that may play havoc with your scheduling\error notification systems with very frequent updates but I would only have 2 or 3 bands per day and it would not be updating on every call. I know this can be worked around with multi sensors and different notification schedules but it is a long way around.