No doubt there's a "canned" answer for this "canned" question, but....
From an energy basis, it should be the same - you need the energy extracted from 200kg of fuel every hour, whether that energy is contained in 200/0.8 litres, or 200/0.75 litres, doesn't matter. (It will if your tanks fill before you can get all the fuel mass you need into them, of course).
That's for flight planning.
If the question were "instantanoeus", it would depend on your engine's fuel system - if it's a FADEC type controlling for a power output, then I'd say it'd stay at 200kg/hr, for the same reasons of energy/power considerations. If your throttle is controlling fuel flow (which would be likely volumetric) then it'd drop by the 0.75/0.80 ratio (as would your engine power output) and you'd end up having to advance your throttle to get back to 200kg/hr at a higher volume flow rate.