Hi Stuart,
there are three SAP standard solutions to enhance PPF Action conditions. Using BADI CONTAINER PPF is one of them. Using BADI EVAL_SCHEDCOND_PPF or EVAL_STARTCOND_PPF is another solution.
However, the most simple solution is to enhance the BOR object providing context sensitive attributes which can be combined and evalutated. In most cases the enhancement can be done without development. In my opinion this solution is the most consultant friendly one.
Because I could not find any guide explaining this solution in a good and development free manner, I created an own one. Please be free to use it too.
http://www.hybrid-eichhoernchen.de/ppf-action-condition-enhancement/
To detect user Status changes you just need attributes for old and new user status. Then you are able to compare both values in start or schedule conditions.
Kind regards,
Peter