On the 332l Super Puma helicopters there is a training limiting box that restricts the max rpm to one engine. The object of this is to reduce the time that the engine spends at Max Contingency during its overhaul life. To keep the andreneline levels correct engine failures are done at a lower calculated weight but the box gives the same engine and rotor reactions as it would if it was at higher weights. Basically you do not have to ballast an aircraft up to MUW to find out how it reacts at that weight with an engine failure; the engine restriction brings the same result at a lower weight.
A civil engine can have a Max Con limit of 2.5 minutes. When that's gone, it's gone and the engine comes out. A military engine, regularly banged up to Max Con during trainng would be unlikely to reach its TBO either. Not the sort of thing to find out when you need it.