Unless anyone else comes up with a better solution, you could try cutting the ferrule in half lengthways and then gently open it up, which will, hopefully, allow you to remove it from the braid. At this point you will see how it was secured (e.g. pins or serrations etc. inside the ferrule) to the braid which may lead to you being able to braze the ferrule up and refit it onto the shortened cable or alternatively it may only be possible to close the ferrule up on the braid without it having been brazed and then fill the cuts up with cold cast bronze.