I assume (though I'm not certain) that if a fuse register - e.g. one of the secure boot ones - is written to then 1s cannot be subsequently changed back to 0s.
But if you write 1's in two operations, does it result in an OR of the values?
In other words, does
fuse prog -y 3 0 0x00000001; fuse prog -y 3 0 0x00000010
give the same result as
fuse prog -y 3 0 0x00000011