If you like to swap decorating tips without swapping colours, use a coupler!
Unscrew the coupler collar and drop your coupler into the bag. Cut the bag if necessary to allow the screw thread to poke through. Place your icing top on the end of the coupler, and replace the collar.
The Wilton Standard Coupler works with all standard-sized tips and is recommended for bags from 30cm/12in to 40cm/16in in size.