* There is a better way to open the enclosure without damaging the edge: using a pliers to push the two sides apart where the bunny ears lift up (google for videos).
* The cable can actually be threaded through the rubber/plastic grommet if you have the patience to remove the broken cable from it and make the two small holes bigger with a drill bit. This can be frustrating but is the only way to keep the original appearance. Be sure to leave enough cable after the grommet for soldering.
* Thin (2-3mm) heat shrink is a good way to insulate the exposed wire after threading it through the grommet.
* If you trust your soldering skills, consider de-soldering the old cables from the terminals.
* Applying a little super glue along the edge and clamping for a few hours is all that is needed to keep it closed permanently.