You can change as many of the Drum sounds as you wish, within the 'Drum Sound Edit' facility, but you can only have one overall 'User Kit' at a time.
Contrary to what I said in my earlier post, it doesn't seem that the User Kit can be saved to SD Card or Disk. I tried editing some of the sounds and Writing to the User Kit and doing a 'Performance' save to SD Card. I then did a further edit of the User Kit, wrote to the User Kit again and saved to another location on SD Card.
I then loaded from SD Card, the file which contained the Initial edited User Kit, but when I played the User Kit, it still played the Second edit. This would lead me to conclude that the User Kit is not included in the data which is saved to SD Card or Disk, but is only saved in KN7000 memory.

I'm not too sure about the actual data retention time for the User Kit memory, since this is not directly stated in the manual, but it is certainly maintained through a Power Off period of 2 hours. The Manual states that Sound memory is retained 'for about a week' so maybe this also applies to the User Kit - I don't know because it's not a facility I've ever used

If Alec is reading this post, maybe he can provide some more information...................

You are quite right about the lack of information in the Manual, about User kits. Unfortunately, it's not the only item which is either not covered, or not covered adequately in the KN7000 Manual.

However, Alec Pagida has written two excellent Extended Manuals called "How Do I Do That" and 'Getting the Most from your KN7000". The first one was originally written for the KN6000/6500 but the great majority of the content is applicable to the KN7000.
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