Adding chainloader stanzas to Grub

[白い熊＠相撲道]

Hello:

Is there a way to add full chainloader stanzas to Grub via the sysconfig file 
through system reconfigure in GuixSD. 

I'd like to have for instance the following entry added: 

menuentry "PureOS on /dev/sda2" {
   set root=(hd0,9)
   chainloader +1
   }

Can I do this? 
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白い熊＠相撲道