The client push didnt work thats because your SCCM DB is still knowing the client as installed, meaning your client = 1 in your site DB. When you enable clear install flag, if the client does not send heartbeat to your site server, this task will set that Client = 0 in site DB. Meaning that system is no more sccm client, and your client push will work on the system. Just make sure when the install flag is enabled, you enable Heartbeat discovery with period shorter than the client discovery period (in clear install flag properties).