how to stop users from stopping radmin server or change settings using GPO?

> or can i modify the radmin msi file to do that?

In MSI by limiting permissions on the installed files, so if stopping the server involves running some program, or modifying files involves editing a file, that's who it's possible. But local admin users probably still can kill any process from task manager. For more detailed answer, you'll have to explain how it is possible to stop your radmin server and how to change the settings.

you can either right click the icon on the tray and then click "Stop radmin server" or "settings for Radmin server".
and another way: go to all programs => Radmin server 3 => Stop radmin server or settings for Radmin server.

i don't want users to be able to do that.
thank you for the help.

radmin-stop-server.bmp
radmin-stop-server2.bmp

I think, only if radmin server¹ has setting like "show tray icon". If that setting exists and is controlled by registry setting, then it's possible to create transform with that registry setting, so when it's installed, it does not show tray icon.

¹) of which I have no idea

it doesn't have such a setting.
but even if it does how can i change the registry from the GPO?
when i go to Computer configurations => windows settings => security settings => registry, and i right click it then click add key, it gives me the keys without the ability to modify them.
i want to add the registry key because i can modify its security settings, take all privileges from the users and just give them to the administrators, but nothing happened.
see the photo attached.
reg-radmin-GPO.bmp

You don't change registry setting from GPO. You would alter installation package so that the installation would install that registry setting. For that, you would create so called Transform, which would be then deployed along with the installation - see tab "modifications" in the deployment package. But if there's no such setting in the program, there's absolutely nothing you can do. If the program is programmed to do X no matter what, then the only way to preclude it  from that is not to run the program. Even if you somehow managed to block program's access to the tray, it would almost certainly crash, since it's programmed to use it.

this is exactly what i did, but it gave me a mixed results, some users in a specific computers can stop the server and some can't.
i'm totally lost.
but thank you for the help.