Perhaps a bit late in the day but in defence of Merlin whose comment has been removed and remaining only a disputed quote from it, just last week I confirmed with Gas Safe, Calor, and a Gas Safe registered LPG fitter, as well as reading the actual written law, that you can remove and replace a butane flexible butane hose yourself (it is exempted in the written law) not surprising as you are obliged to check the hose condition regularly and change it when necessary.
It appears therefore that as long as you didn't touch the fixed part, if there is one, of the installation, if you can remove the flexible pipe yourself it follows you should be able to substitute an old Butane prepared cooker for a new one, just as you are able to fit the hose and cylinder you are using in an old heater to a new butane heater.