If you're talking about adding it to the Workbench Tools menu, you can get "AddTools" from Aminet and this allows you to easily add commands to the Tools menu.
So for example, using Skick to boot 1.3, I would just add these lines to the AddTools text config file:
Boot WB 1.3
c:skick kick34005.A500
A
...and that's it. Then when I select "Boot WB 1.3" from the Tools menu, it'll automatically reboot with the 1.3 insert disk screen.