First what you probably mean os updating a processinstances (that is what you want) to run with the latest (at that time) processdefinition. Secondly, this has been discussed in the forum before.
You have to learn the jbpm object model and probably some of he database model to be able to do this.
Some generic design tips for processes:
- keep them short as possible. As an example I always say there is no 'mortgage process' just a mortgage in some 'sleeping' state. In this state it is referencing specific versions of services and or small process which need to run if something changes. Much simpler
- Keep your domain model out of the process as much as possible
- Rethink if really, really need to update the processinstances. Think out of the box when designing the process initially
It sounds like you want some type of effective date either on the process instances or on the task nodes themselves.