Yes, there are emulators that will show the hex code, but unless you know ASM it won't do much good.

Avoid Nesticle. It's very inaccurate and allows a whole bunch of bad behavior that will make your hack fail in most other emulators.

Nestopia(Though if you have a slow PC, it'd be a bad idea to use this one.) is good, FCEUX is nice too.

The simplest way? Castrate the controller input.

Find out how the NES reads the joypad; assuming it's a register, set a breakpoint to that register and trace through the code you find. It'll take some intuition, but along the way you should find some sort of test (likely a CMP instruction) to see whether down and A are being pressed at the same time: maybe the routine sets flags as to which buttons are pressed and later checks them, or maybe it just takes the raw joypad register; I dunno. But once you find the test, it will be followed by a conditional branch. If the conditional branch is set to branch if down and A are being pressed, you'll want to NOP it. If it's set to branch if down and A are not being pressed, you'll want to change it to a permanent branch (BRA) instruction.

For the american version of the ROM, change $3d3b4 to $3d3b7 in the ROM to $EA. 

For the Japanese version, set $3d3b0 to $3d3b3 to $EA.

Thanks to all  :thumbsup:, your help is awesome i finally remove the slide movement, i want to take experience game like rockman 1-2-9 thats all.
Well principally i have intention to publicate this hack because no are much rockman 3`s hacks rom, no are awesome than others hacks of rockman but i think is funny, basically mi hack contents:

-No slide movement, make the game like rockman 2 more harder but no much
-New levels edit and graphics
-New normal enemyes sprites
-Modify normal enemies weakness for weapons
-Modify boss sprites and color (a little but new robots masters)
-Modify boss weakness (another way to beat the game, no like the original)
-Diferent sprites for weapons (for example the snakes now are bubbles)
-Diferent music for the stages (but is the same music of rockman 3, i think this bgm is great and change the music is a lot hard)
-New sprites faces for the select bosses

And no more for now, only i need to modify a little the fight patterns of the boss, is dificult to find the hex for this, but ill try, all help is necesary please and thanks  :thumbsup:

Random question unrelated to topic: (sorry)
Are you japanese or something? I was just curious that's all. Cause only they ever say "hack rom" instead of rom hack

What about UPS?