> In this case, I would like to manage things with guix. And I want a specific file-system to be mounted at a specific mount-point (home directory), upon every boot.

I think the best way to do this is to use Guix to set the right Udev
rules for Udisks:

https://wiki.archlinux.org/index.php/Udisks

> The directory becomes writable only by root. I am able to manually change the permissions, but it resets on every boot.

Weird, it should stick.

-- 
Pierre Neidhardt
https://ambrevar.xyz/