I created 7 slaves sites that use the same template. The template has seven different backgrounds params.ini configurability from the file, but if I use the special copy I can not configure it, because it changes the background as the template. I am forced to copy the template on each slave! How can I fix without having to copy the template on each slave?

If you are using Templates that are using standard joomla processing, the "params.ini" files become specific to each slave site event when you use the "special copy" of the tempaltes directory.

By default, when a "params_{site_id}.ini" file does not exists, it read the "params.ini" file that is the master one.

Some templates company may have created specific framework that bypass the standard joomla processing and that miight read the "params.ini" file instead of the "params_{site_id}.ini" file.

So this repends of the template that you are using.

In the Master site folder templates>name templates> i have the new 7 file params.ini "params_site_id.ini". But the new 7 slave site read the old normal params.ini.
I try with the template standard "rhuk_milkyway" but i have the same problem.
How do i read the new file with the new extension params_site id.ini ?
Sorry for my bad english, i'm italian...

Check that you have correctly installed the JMS patches.

I have retested with the "rhuk_milkyway" in which i selected another color and with works perfectly

I am having the same issues. I ended up removing that JMS patch so that parami.ini works correctly. I know this is not a good idea but I was left with no other choice.

Removing the JMS patch will result to share the parameters for all the websites.
As long as I don't have a scenario that allow reproducing it, I can not give you a better diagnosis.

Perhaps there is another settings that affect that.
So try give me a very detailled scenario and procedure that show how to reproduce it.