Things I'm seeing testing a Rogue
There is a byte in the save file that is non-zero only for Rogues. It might have some effect on the percentage of times you get the "Disarm Failed!" message when disarming a trap. As opposed to actually setting off the trap. But it might be the level of the Rogue instead. It took me until level 32 to max out the byte at FF, and even then sometimes my rogue sets off traps when disarming.
Hide in Shadows seems to ALWAYS work, unless the Rogue is the only one in the party left alive. Then it NEVER works. Rogues also get hit by Dragon's Breath, even if the hide succeeds.
I can't see that the Theif Dagger [sic] does anything. It didn't seem to make any difference when I was hiding in the shadows, and it didn't seem to make any difference when examining, disarming, or opening traps. It didn't seem to make any difference when I ran over a trap, either.