JMeter Properties can be used to parameterize your test. One version of your script can then be used in several different test configurations. JMeter properties also allow you to make mid-test changes to script behavior.
Setting JMeter Properties
Set these parameters before the test launch in the JMeter Properties section of the test create screen.
To set the value of a JMeter property, slide the toggle to "on" and enter the property and value:
To add additional property/value pairs, just click the (+) at the right of the section header:
Changing JMeter Properties mid-test with Remote Control
You can change JMeter Properties mid-test with the Remote Control button in the live reporting screen. For a short video and two examples, have a look at JMeter Properties (Real Time Control).