1. The Principle diverted out tuition to his personal use - a family pilgramage to Mecca.
The Principal diverted tuition fees for his personal use- a family pilgrimage to Mecca.
2. Owing to the commander's diversion strategy, we averted a total defeat.
you could say 'Commander' if youwanted to
3. Beginning in September, the University will revert to the semester academic system.
I'd be tempted to use 'from September'