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
That’s correct. As fuses cannot go back from 1 to 0, it would be equivalent to an OR. You should be able to do this on the i.MX6 without problem.
However, this may not be true for other One Time Programmable memories in the market depending on their features.