Are you talking about SSD 4? Because you can fully map everything there! You have to think the other way round than you usually would. I don't have the plugin in front of me right now but from the top of my head:
go to the Mapping screen. Now you see the various instruments and their articulations on a list of midi-keys.
Now you can hit one of your pads (let's say the snare) and you will see a midinumber light up whenever you do so. Let's say your midinumber for the snare is C1.
What you should do now, is check on the list what Slate's midinumber for the a snarehit is. Let's say it is A1.
What you should do now is NOT to put C1 next to the Slate-defined midinumber, but go to C1, and route that to A1 by setting it to A1 in the second box (there should be 2 boxes next to eachother, the left is the original note, and the right is where it gets sent too). Whenever you hit your snarepad now, the midinumber you send (C1) will be routed to Slate's snare-midinumber (A1). This way you could even route multiple pads to a single instrument, if for some reason you desire to do so.
It probably sounds a lot more convoluted than it is. Just make sure to save your midimap every now and then, because this part of the process was very crash-sensitive for me. Also, make sure you don't create routing-loops, because that crashes the program every time for me.
Good luck and enjoy!
