Yes you can. I removed/washed PureOS of my Librem 14 last week then i burned GNU Trisquel Aramo (T11) and worked really really nice. To install GNUFSFRMST11 type: “help” in Seabios.
http://cdbuilds.trisquel.org/aramo/trisquel_11.0_amd64.iso
The main reason to remove PureOS was that i am not fan of Apple/Gnome shell.