Actually you don't need a script for this. Open Kontakt for editing and make sure you've got
all the Groups selected. To do that open the Group Editor and select the first group, then
scroll down to the bottom of the groups and Shift+Left-Click on the last group. Then make sure
you've got "Edit all groups" on.
Now go to the "Source" module and click on the "add mondulator" button and select LFO. Use
what ever wave shape you want, that can be changed later.
In my Steel Guitar, I also applied a LFO to the Volume in the Amplifier module, I kind of liked
the way the two of them sounded together. However, you don't have to do that to get vibrato.
Adjust the intensity slider, on the "Source LFO", I've got it set at 0.61%, but you can come back
and experiment later. For the Volume LFO I used 31.2%.
Then scroll down to the modulator section. Add both an "Intensity" and a "Frequency" to each LFO.
Then select the CC controllers you want to use as I show circled green. Intensity is the amount,
and Frequency is the speed.
That should get you started, you can experiment from there.