So, BB-2124, it appears that your scenario touches on both of my exception examples... not easy decisions. I will add something related that may help you in general. I instituted a "rule of respect" with our players. If they were ever to call/text with communication that they would be late or miss practice, meetings, game, etc., they were to include the specific reason why they would be missing. So, there was always a "I'm going to be late to practice today because...". This afforded the chance to talk about making the right decisions, prioritizing, planning ahead, etc., and I think kept those occurrences to a minimum.
I also made it clear with assistants that any disagreements we had among ourselves was to be kept away from the players. Talk thru it, work it out and come together on a position. Inevitably, there will be things that you will never agree on and, at that point, they have to respect that yours is the final deciding vote and must be supported.
We also had instances where the team would be involved in the process. Depending on the nature of the issue, the player in question may or may not be present. As example, a kid quits and asks the next week if he can come back. Similar to your situation, the kid really benefits from being part of the team, so you look for ways to make an exception. In this instance, I opened it up to the team with the question of whether they can fully support the decision to have him back as a teammate, explained how the player can benefit from being part of the program and how each of them had the opportunity to be a positive influence on this player. I also explained to the player individually and to the team separately that he would have to earn his way back, making up for lost time and regaining the trust of his teammates that he is as committed as they. Maybe there is a way to rally your team around supporting this kid. But I agree that you have to be careful about how you go about opening that door and to what extent.
Lastly, i believe it is never a good idea to have a different set of rules for starters and non-starters. Everyone has an important role in a program and no one should be above or below the program guidelines. Besides, aren't the non-starters trying to become the starters?