Today I need to type a long string into a VNC window, without the almost ubiquitous functionality of copy and past to window.

This just works under XServer and not Wayland because the use of xdotool.

STRING="yum install https://rpms.remirepo.net/enterprise/remi-release-7.rpm"
WID=$(xdotool search --name "centos7.0 on QEMU/KVM User session" )

xdotool windowactivate --sync "${WID}"  
xdotool windowfocus --sync "${WID}"  
sleep 0.5
xdotool getwindowfocus windowfocus --sync type --window "${WID}" "${STRING}"
sleep 0.5
xdotool key --window "${1}" KP_Enter

Maybe, on day I will change this to ydotool to work also under Wayland.