As I understand it, to create a script to run on a single site you can only use a deploy script, however when you create a deploy script in a site, it is attached to that site only and nmot available to other sites, meaning you have to duplicate the same script in every site you want to run it on.

Global script and marketplace scripts can only be run per server. I would like to add a global script to be able to run on specific sites rather than specific servers. It would be awesome if on the edit/run script page after selecting a server it had the opportunity to select specific sites from that server and only run the script on those sites, or show global scripts in the deploy scripts dropdown to run on that speific site