I'll have what he's having! FE Hoppy is bang on the mark.
FE Hoppy,
Without a doubt that is one of the easiest and clearest answers to a question that i have seen on the prune yet. I knew what needed to be said(even had a crack at typing a draft) but sometimes getting what's in your head and onto a computer screen for a wordwide audience to read can be a little difficult. Well done. Clear, concise and to the point without going too deep and getting too technical.
I'll just add that the method of de-rating the engines desribed above is called the "assumed temperature" method of de-rate.
Some aircraft/engine combinations have settings for specific de-rate levels. 767 for example. You'll find settings for "de-rate 1" and "de-rate 2" which limit thrust levels by a set percentage. This de-rate can also be used for climb thrust de-rate levels in addition to take-off.