If you don't need PurePaths for the time being then simply un-check the 'Capture Events' for that agent from the System Profile Edit > Agent Mapping > Select the Agent and then in the left bottom side you will find the option 'Capture Events'.
What are you looking to accomplish by blocking the connection? Are you looking to avoid the slight cost of the agent on the server or just trying to free up a license? If it's the former you would need to remove the agent from the process, this is the only way I'm aware of to stop the agent from reaching out to the collector/server. If you'd like to free up a license you can try modifying the mapping the agent group is looking for so that it no longer matches, then when you restart the agent (or collector) it will no longer map and a license will not be used - the agent will still be there though and it will show up in the agents overview as not mapping.
So apart from removing the agent/modifying the agent config to point to a nonsense server/collector I don't think there is a way to "block" the connection within App Mon.
There is not a shortcut to achieve this but you can commenting out the command-line argument.
Some more information you can find from the following post: