Sometimes the need exists to submit a yml based test but to modify the concurrency on the fly to see how it impacts test results.
Here is how this can be accomplished
1. Change the starting file of your test to be the JMeter JMX file (temporarily) by selecting it in the scenario definition. It will cause the green arrow to be pointing to it.
2. Set JMeter property BM_CTG_TargetLevel to the initial concurrency as described in this article. Note it must be this particular property as this is the concurrency value of the concurrency thread group that Blazemeter converts your JMX into.
3. Change the starting file back to the yml file.
4. Start the test. When it is active you will notice the Run Control button at the top right:
5. When you press it, it will allow you to change the value of BM_CTG_TargetLevel to a different concurrency while the test is running, as described in this article:
6. Soon the Timeline report and Summary report will reflect the changed concurrency.