Yes, you are correct, the engine will run at the same temp but the 88C thermo will open slightly later than the 82C thermo.
Diesel engines like to be hot (around 100C) and need cooling (radiators, water jackets, pumps etc) so they don't get hot...
My 92 200tdi Defender has the original engine. Recently replaced the thermostat with a new one that was rated at 88 C. The engine is now running hotter than it always has previously. I’ve checked and some people are saying the 200tdi should have...