I'm new to yocto as well but what we do is in our own custom image:

inherit extrausers
EXTRA_USERS_PARAMS = " useradd nodered"

and then since we use systemd we've created our own service file that includes:

User=nodered

in the [service] block definition, so the executable is run using that user instead of root.

Extrausers docs are https://www.yoctoproject.org/docs/current/mega-manual/mega-manual.html#ref-classes-extrausers

An alternative you might look at is the useradd class https://git.yoctoproject.org/cgit.cgi/poky/tree/meta-skeleton/recipes-skeleton/useradd/useradd-example.bb which probably lets you set the users in your own recipe instead at image level