I am not sure I fully understand your question, but here is my best answer. If you do not configure a sensor on an agent and run hot sensor placement, the agent will be unchanged. This mainly applies in scenarios where you have configured a new sensor on an agent group and you run hot sensor placement for that system profile. The sensors are only added to the agent groups that have the sensor pack enabled. This makes it very important to choose which sensor pack you add new sensors to or to create new ones for better grouping of similar sensors.
Hope that helps,