Thanks for the answer. In the end, I hate to say it, but I've relented and used something other than Kixtart. I am able to deploy BGINFO via group policies and can also set up a scheduled task via GPO to run it on a regular basis too. BGINFO does change everything 'on the fly' when it's launched and I can then replace wallpaper when needed for the wallpaper to be changed whilst the user is still logged in.