There's indeed no really straightforward way to do this.
All you can do it to edit your existing rule hostname mask to match your other sites. Use semicolon separated list of hostnames:

I'm pretty sure I'm missing something here, but I just can't find it:

Is there a way to set a particular transfer setting for each site in the site manager configuration? The only option I found is in the dropdown of the "Advanced" button in the site options. It's named "Transfer Settings Rule...". But it opens a completely new transfer setting to fill out. I'd just like to use my existing rules and assign them to my sites. Is that possible?

Thanks a lot,
Roman