Reply to Message

hello everyone,
My question is as follows:
how do I change the toc entries styles to an existing custom style, I know I can use the insert table of contents then choose modify and change the different TOC built-in styles, but I don`t want to change them I want to use a new style.
Also, on the same dialog box there are two buttons that I think will allow me to do exactly what I want: new and delete. But for some reason they are disabled.
Any help would be nice.