There is a used blade in the back of my injector, can it be removed?
Not a good idea to remove the blade entirely from injectors. Best to leave a blade in or replace the blade with a factory blank (dulled).
Getting the blade out without inserting another can damage the razor not to mention the risk of cutting yourself as you need to grab the blade to extract it.
Good habit is to leave your last blade in or make a dull blank to replace the last used blade in the injector.
The main selling point for injectors was safety as you did not need to touch the blade (used or new one)