Conditional Agent availability

It it possible to for an Agent's properties to be marked at runtime to change behavior ?
My 2 scenarios would be

1. By time. Mark an agent only available between a certain period e.g. after hours
2. I have two builds, one on windows and the other on linux. As part of the test execution they communicate to a test peer (database,physical device etc) that can only have a single connection. The agent rule i would like is "run on compatible agent when resource is free".