Restrict certain Plugins to admin only

Hi Guys,

I am running a multi subdomain site and have a plugin that changes the login page.
The problem is that this plugin is available for all users. If I network deactivate it then I cant use it on my main site.
Is there a way to make this plugin available to me only ?

OR..... Is there a way I can customise the login page to appear the same on all created sites ?

Thanks