Hi Daniela,

Have you tried './pre-inst-env guix build ...' instead of 'guix build
...'?

The difference is that the former command will look for package
definitions in your checked out, and modified, version of Guix. 

The latter command looks for package definitions in your installed
version of Guix.  Your modifications will be seen by this command after
you submit a patch, it is committed, then you update your installed
version with a 'guix pull'.

Best regards,

Paul.