Tmux 2.3 adds a useful option called ‘pane-border-status‘. However I could not find out how to set pane title.  My walk around is as below

cat ~/mylocal/bin/setpane
#!/usr/bin/env csh
printf ‘\033]2;%s\033\\’ $1
tmux set-option -g pane-border-format ‘#{pane_index} “#{pane_title}”‘

This script cannot be called within Tcl. Hope tmux will add a ‘rename-pane’ command in the future.