Altering initial UID/GID of default "DietPi" user

General Discussion
1

I’m trying to find the “first boot” file that creates the “DietPi” user -
I’d like to make sure that this “user” ends up with an identity outside the standard “userspace” id numbers –
OR
I’d like to be able to make sure that UID/GID ==> 1000/1000 has a specific username so that scripts for some of my software installs will work properly.

Help ?
so far – this is what I’ve done in trying to find things
verifying that the “freshly made” dietpi boot media is mounted

find /media/$USERNAME/$mediaID -type f -iname “*.txt” -exec grep -Hine “adduser” {} ;
find /media/username/mediaID/dietpi -type f -exec grep -Hine “adduser” {} ;

and so on — have not had much luck

I would have thought the “preboot” file or dietpi-autostart
or the default dietpi.txt — nope…

2

User is part of the image already and not created during initial boot/setup.

and this is the related function

As there is no other regular user yet, the UID 1000 is automatically used.