Para inserir copy-mode
pressionando PgUp (sem o prefixo), você precisa disso:
bind-key -T root PageUp copy-mode -u
Na seção manpage, em bind-key
:
The root table is used for keys pressed without the prefix key: binding ‘c’ to new-window in the root table (not recommended) means a plain ‘c’ will create a new window. -n is an alias for -T root.