Set value when saving a work item type (User Story)
Accepted answer
A precondition can't give you that, because a precondition runs before (pre...) the save. It also is a condition which pretty much says that it guards the save and can prevent it.
You want a follow up action aka a participant.
https://jazz.net/library/article/1000/
Examples see: https://rsjazz.wordpress.com/?s=participant
Most relevant: https://rsjazz.wordpress.com/2012/11/27/resolve-parent-if-all-children-are-resolved-participant/ and https://rsjazz.wordpress.com/2012/07/31/rtc-update-parent-duration-estimation-and-effort-participant/ and https://rsjazz.wordpress.com/2012/08/20/manipulationg-work-item-enumeration-values/
Also: https://rsjazz.wordpress.com/2012/12/14/do-not-modify-the-triggering-element-in-an-operationadvisor/
You want a follow up action aka a participant.
https://jazz.net/library/article/1000/
Examples see: https://rsjazz.wordpress.com/?s=participant
Most relevant: https://rsjazz.wordpress.com/2012/11/27/resolve-parent-if-all-children-are-resolved-participant/ and https://rsjazz.wordpress.com/2012/07/31/rtc-update-parent-duration-estimation-and-effort-participant/ and https://rsjazz.wordpress.com/2012/08/20/manipulationg-work-item-enumeration-values/
Also: https://rsjazz.wordpress.com/2012/12/14/do-not-modify-the-triggering-element-in-an-operationadvisor/