Nikon have a look at the dcl I made using Multi Radio Buttons.lsp, when you select a button, the variable BUT is returned with the button number, so you can use a cond looking at the BUT value, for the {} just need a
(cond
((= but 1)(setq str (strcat (chr 92) (chr 123)) txt (strcat (chr 92) (chr 125)))))
((= but 2)(setq str (strcat "[" txt "]")))
....
)