Is it possible to prevent users from self registering in system manager sentry enrollment?

[Net]

I want to prevent a user from registering on the system manager in wifi. Is it possible to hide the splash page showing the registration screen?. If the user has a system manager install Internet access will be provided or else the block message or something will appear or no internet access. 

[Net]

If this option is enabled it will open the splash page which gives the ability to the user to install the system manager agent. It is a disadvantage as we have limited licenses. Is there a way to block that splash page and also check for system manager installed in device or not?