I have seen a lot of good advice in this thread.
With regard to threats of suit, a soft touch might be the best approach. In some situations a postscript might not be soft enough. Like it or not, sometimes people do get defensive. Lots of people who would otherwise settle shut down when openly threatened.
So much so, in fact, that it might be best to disguise a legal threat in a way that only dawned on the target after reflection. Unsettling dreams might reveal litigatory acrostics to sweat-soaked school admins, who would suddenly cave to all demands in the knowledge that their petty bureaucratic pretensions were outmatched by truly Machiavellian guile. Even slightly awkward wordings or phrasings might serve a useful purpose, in tipping off the reader that there was more than met the eye.
