Hi Mickael! Currently there's not a great way to do this in Prefect. We're looking into features around flow priority, and this may be available in the future. If you have any further details around your use case, we'd love to hear them as we think about this feature!
Labels on Flows can control which agent picks up task execution, but these aren't dynamic.
https://docs.prefect.io/orchestration/agents/overview.html#labels