You mean change the key, not change the scale, which is what confused me.
What you want to do is this. On the Triton Extreme, you're probably playing in combi or program mode, right? If so, you can set the transposition of any/all timbres in a combi individually, or you can set the transposition of the oscillator(s) in the current program. Do this, and save a new copy of your combi or program. Have the KN 700 pick the new combi or program whenever you do a program change instead of the old one.
Basically, what you're going to be doing is saving the transposition into the sound you use for a particular song so that you don't have to call it up on the Triton Extreme.
However, it sounds like you're trying to play everything in one key, or at least that you don't like the key they're singing in. I'd suggest you try to learn your parts in the keys your singers are going to use; transposition often has its own set of issues. I've been playing at church before where a particularly weak pianist transpose the digital piano for a song and didn't switch back, throwing everyone else off. If you really can't handle playing in the key they want to sing in and you can't get them to move a half-step up or down, then try to build your transpositions into your programs like I said so that it's automated for you, but ideally, just learn to play in their key.