When my customers come in needing a microphone replaced, for instance, and their screen is cracked I always warn them that it may crack more and need to be replaced after the repair. In your case, of course, the only person you have to worry about it yourself since it is your device. Having an already broken screen makes it a lot easier to break the screen even more (probably physics or something). But it is definitely possible to remove without causing any more damage to the broken screen. You may have to heat the device several times and have plenty of patience with it, but it is certainly doable. And even though it is cracked, it should be able to go right back on once the repair is complete. You will need to be extra cautious around the cracked area and make sure it is thoroughly heated to help with the removal. Even if it does crack more, most often it will still be functional as long as the digitizer and OLED aren't damaged. I hope this helped!