Actually they probably can be replaced but I suspect the cost would be more than a new pair of skis. Granite Chief in Squaw Valley has a ski building press and can re-build and relaminate a pair of your favorite skis complete with your own graphics. I considered this a long time ago with my old Rossi Strato's (the great purple skis) The rebuild would have included new bases, new topskin and new edges but the price did not warrant the gain.
blowout repairs if the edge is not broken costs about 100.00 and the ski is pressed under high pressure. and the base is repaired with a patch and then retuned. Beware of anyone offering to repair an edge blow out by putting a screw in the edge to keep it tight.