Jihad spamming is a notorious exploit. Unlike crusades you can launch multiple jihads at a target. It is ridiculously powerful when exploited in this way.

Spy spamming is the technique where massed spies are dropped in an enemy province. The highest valour spy causes a revolt, but all others gain valour as a result.

Assassin spamming is the training over of large numbers of assassins and sending them all against a target in the hope that one will succeed. This isn't really so much of an exploit, especially if there's a border fort in the rival faction's province, but as you've said you're removing these then this could be an issue.