I am afraid that's not correct information.
To validate I just tested this scenario in my environment where two agents were already connected to the EM reporting more than 400 metrics each.
-Modified the clamp setting introscope.enterprisemanager.agent.metrics.limit to 100 and saved changes
-Waited for a minute before event was generated and agents were clamped
-Is Clamped metric still reported 0
-Reversed the changed to clamp value and event was resolved as well as agent icon changed
Scenario 2:
-Modified the clamp setting introscope.enterprisemanager.agent.metrics.limit to 100 and saved changes
-Waited for a minute before event was generated and agents were clamped
-Ran some transactions on agent so new metric is generated
-Is Clamped metric changed to 1
-Reversed the changed to clamp value and event was resolved as well as agent icon changed
-Is Clamped metric went down to 0
Conclusion:
-Event does NOT require EM to be restarted to be cleared
-Is Clamped metric can report 0 values even when Agent is clamped because it's only evaluated\regenerated when new metric for agent comes in however if it's reporting a value of 1 already and then clamp value is changed then the reverse is done without above requirement.
Hope this helps. If there are still further questions please engage CA APM Support team.
Regards,
Kulbir.