How to change the store location

[Jean-Christophe HAESSIG]

Hi,

I'm experimenting with Guix to use it on an HPC cluster. In the docs it 
is written that the store's *default* location is /gnu/store/ but I 
can't find how that location ca be changed. Same for /var/guix.

As for the 'why', it would matter if Guix was used for sharing software 
between nodes so that users can find their profile on any node, and 
using Guix at the same time to manage system software on nodes.
That way, the node can (re)start even if the network shares for users 
are unavailable for some reason.

Thank you,
J.C. Haessig