RAM 0x09 = first letter of name select, break on read here
see rhdn for table
offsets are at the start of the opcode, not necessarily where the exact number is
findings using fceux debugger
check if your name is "erdrick" and get mad if so:
letter 1:
1bc1a = compare $29; E
1bc1e = compare $0F; e
if true jump to ram $bc13 - letter 2
otherwise rts and proceed
letter 2:
increment x
load appropriate byte for current letter
compare with the listed byte below, continue on if true
this repeats for the remaining letters
1bc26 = $36; R
1bc2a = $1c; r
letter 3:
1bc32 = $28; D
1bc36 = $0e; d
letter 4:
1bc3e = $36; R
1bc42 = $1c; r
letter 5:
1bc4a = $2d; I
1bc4e = $13; i
letter 6:
1bc56 = $27; C
1bc5a = $0d; c
letter 7:
1bc62 = $2f; K
1bc66 = $15; k
if things are still true at this point,
jump to ram $bc5b
x is incremented and compared to 0x8
if it's not 8, branch to $bc61
if it is, return; hence "erdrick " is fine
load letter 8 into a, if it's zero, jump to ram $bc5b
this time x will equal 8, so it returns
by this time the game's determined you've tried to name erdrick "erdrick" and it gets annoyed and pops up a message shouting "INPUT YOUR NAME!" emphasis on "YOUR", presumably

there's probably a more elegant way to change this, but i just simply zeroed out all the comparisons
if you want to block a different name, leave any excess letters zeroed out
say you want to negate "loto" instead, then change the first four letters to correspond to that, and set the other three to zero
if you want to block an eight character name, you're out of luck without some actual modifications to the code