Hi, there are three ways to do this.
You can save a User Preset in Vintage D itself, or save a Kontakt Snapshot, or save a Kontakt Instrument.
The presets are in the bottom left corner of the Vintage D instrument windo. You can click on that and then it'll have a window for user presets, where you can save one. Upon loading Kontakt and Vintage D, you can then load that User preset using the same menu. Those presets are saved at:
C:\Users\NAME\Documents\Galaxy Vintage D\Data
Kontakt snapshots are made by clicking on the camera symbol in the upper part of the instrument window besides the "i" symbol (to the left of the "tune" knob). Those can also be loaded upon loading Kontakt and the instrument via the same button. They are saved at:
C:\Users\NAME\Documents\Native Instruments\User Content\Galaxy Vintage D
For saving a new instrument (which is what MacMacMac wrote above), click on the Floppy Disk symbol on the right side of the upper Kontakt bar: This saves the entire instrument file into the same "instruments" folder inside your library install folder. When launching Kontakt, it'll then show up in the instrument browser where you can simply load it, and it'll have all settings applied right from the start. So this might be the most convenient method. (note though: you can only load these instruments with the same or higher version of Kontakt as they were saved with)
If you change the amount of voices, it looks like only saving a Kontakt instrument will preserve this setting. If you do it and then save settings with the other two methods, it'll always revert to the default amount upon load.