I would say the most important thing to consider after clearance is how well controlled their blood sugar levels are throughout the day. It is important for them to keep track of their blood sugar reaction to exercise sessions and to relay this information to their physician for guidance in adjusting their medication accordingly. I recommend they take classes on lifestyle adjustments for people living with diabetes. Many have taken the class prior to deciding to work with a fitness instructor, but I recommend they contact the teacher again and discuss the change in activity if applicable. In general, there isn’t much difference in program design or implimentation. I have worked with people with diabetes who achieved amazing results and even several athletes. While not the norm, these clients had no problem with very high intensity training.
Also, education (my mantra) is always the most important part of working with clients who have challenges. You can never learn too much. Good luck.