When copying multiple selection with shift+F5, we can add a suffix for each selected item:

What is interesting is that if you try to insert a string as a prefix, each character of the prefix will replace the existing character on the corresponding position in the existing file name. For example, "abc*.*" applied on "test.txt" will rename to "abct.txt".
Anyway, if an option of copying with renaming is desired, it should be implement via FC rename tool, which is more powerful (so instead of renaming the files in the active panel, the files with the new names will be copied (or moved) into the folder in inactive panel).