Can I half the current rating when moving from 100-240V to just 230V?
Dangerous. Very dangerous.

Changing parts like bridge rectifiers and fuses to lower-rated ones will not only invalidate any warranty (if there was one) but will make the device no longer safety-certified, meaning if your house burns down you have no one to sue except yourself and may even be denied insurance benefits.

The fuse is meant to withstand normal operation, start-up inrush current (which is usually higher than the max steady-state current) as well as nasty things line line dips and interruptions, brownouts, etc. - you may get lots of nuisance fuse blows, especially if you draw heavy power from the PSU. Never change the rating or the type of fuse - there are fast, normal, slow-blow types (among others) and were carefully chosen for the application.

The bridge has to withstand these same transients. Blowing the bridge can do lots of downstream damage (it could take out the DC/DC converters) rendering your power supply essentially useless.

Furthermore, can you 100% unequivocally guarantee that no one would ever attempt to use this PSU at 100VAC? Would you disable the input range switches and hard-wire the PSU for 230VAC?