That should be fairly in line with control replacement/alteration hacks, though will see you want to get hands on with some assembly code. Bonus today is you are only wanting it for the one action rather than all of them so that means a bit less work; sometimes if we have dead button or game wide swaps it ends up a pain as you get to hunt down menus, bonus modes and more besides on top of whatever main game actions.
I doubt there will be a control swap or control customisation but if there are then that can change things, even if the swaps are a minor thing with nothing to do with dashing.
Such a thing is also harder to work around at emulator level or even with hardware hacks so there is that too.
There will be something that checks the button press (or in this case consecutive presses). I don't know if the game will debounce or read straight from the buttons, though if it does a scan on the buttons will still get you somewhere.
The button combo stuff can be harder as the game will not be this is pressed therefore and instead it will probably do some kind of note it was pressed, then a check to see it was released and then another check. There will possibly be a timer to have it time out after so many frames, however it should be started with the first press so there is that.
In the end you are still calling a function that would be called after the double press, and instead having a simple press (hope you have a spare button) be the thing that calls it.
Tutorial then would be something like
Set a break on read to the button location in memory https://wiki.superfamicom.org/controllers
Probably every frame/vblank will be a thing that checks this.
It will determine buttons are pressed and then call the corresponding functions. It might do something on them first to check if just the button it cares about is pressed (don't know the SNES but other systems might use a logical AND with the value and just the one it cares about, if the result is positive then it was pressed and if not then not, alternatively a mask).
Going by a thread the other day it seems the SNES joins some other systems in having a new function called check in its debuggers.
Here the idea would be to start the scan, wait around, walk left, walk right, jump if you want, better if you can have no enemies on the screen or no new hazards appear but it is not so bad if they do...
Basically you are doing everything but dash. That way when you go back to the new function called log after having dashed then it will already have seen the time function do what it does, walking functions, music playing, possibly idle animations and the potentially dozens of other things the game does when you are doing nothing or just moving. Anything new (like the dash) will then be something it has not seen run before and you have the location of the dash function.
You would then work backwards (a break on execute breakpoint being set on the earliest part of the dash) to find the thing looking at controls and change its check to instead possibly remove the timer part and just look at a single button.
Here is one for the NEShttp://www.fceux.com/web/help/fceux.html?TraceLogger.html
In both cases I don't know if double tap left and double tap right are different actions within the game or data passed to the same function but set to go the other way. Easy enough to test these things though.