the idea of exile and losing a tail blade is probably a historical and longstanding tradition. to lose a tail blade would be probably the worst dishonor in andalite custom. This tradition has obviously been around for centuries if not longer and, as seen in the many andalite conversations, (primarily book 8 and HB chronicles) andalites value honor to a great extent.
the relatively new invention of the morphing technology obviously creates the possibility of being able to remorph the tail blade, however, this would probably be the lowest of the low in terms of honor and discovery of an exile with a remorphed tail blade would bring even greater shame on the family lineage and could even be punished by ordering a death sentence for the entire family line so as to remove such dishonor from the andalite bloodline. therefore it can be assumed that remorphing a tail blade after exile would be unthinkable. no doubt andalite scientists are looking into the possibility of being able to remove the morphing technology from someone with the ability who is the n exiled.