Aparentemente, precisei fazer minhas edições em keybindings.tmux.
$ cat ~/.byobu/keybindings.tmux
set -g prefix F12
unbind-key -n C-a
bind-key -n F1 previous-window
bind-key -n F2 next-window
bind-key -n F3 copy-mode
bind-key -n F4 new-window \; rename-window ""
bind-key -n C-F4 display-panes \; split-window -h
bind-key -n S-F4 display-panes \; split-window -v
bind-key -n F5 command-prompt -p "(rename-window)" "rename-window %%"
unbind-key -n F6
Funciona muito bem e mapeia as teclas para combinar vagamente os ícones nas teclas F de um pixel do Chromebook.