When you update SQL Monitor which has Multiple Base Monitors configuration, you will be prompted with an option to keep existing configuration or overwrite it. This option is presented in a "Keep existing base monitors" checkbox. 

When this checkbox is ticked (recommended):

• Existing Multiple Base Monitors configuration is going to be preserved, therefore, it will not be possible to modify it, i.e. change port number (which will be greyed out.) of updated Base Monitor, which is on the same machine.

When this checkbox is not ticked:

• Existing Multiple Base Monitors configuration will be deleted, and the new configuration will only include updated Base Monitor, which is on the same machine.

In addition, in order to fully update existing system (SQL Monitor UI and all Base Monitors), it is essential to update remaining Base Monitors afterwards.