keep the primary fuse the same size... if you go over 1000VA, the fuse will blow... however, adding a ton of output devices is sure to increase current draw... it will increase the idle current. increasing the power supply voltage will increase the thermal stress on any 3-terminal regulators in the power supply, and standing currents in the diff amp and VAS (unless they are using constant current sources).
is there any particular reason for adding output devices and rail voltage? it seems like you are trying to actually increase the output power of the amp, but the limiting factor here will still be the capability of the primary winding of the power transformer. if you are only trying to increase the "dynamic headroom" of the amplifier, that's likely to work (you will also need to increase the voltage rating and capacitance of the main filter caps for it to be effective), but actually increasing the output power won't.
it might be useful to add some pictures of the schematics of this amplifier, because otherwise our comments are conjecture and guesswork.