Redmine

Is there a way to automatically change an issue field? The change should be triggered after modify another issue.
To be more specific: Our issues are organized in groups to solve them serially. For example, in that case

Issue Assigned To
--------------------
task1 -> UserA
task2 -> UserB
task3 -> UserC

1. task1
2. task2
3. task3

UserA completes task1 and then changes task2 to another status, so UserB could be informed to start its task.

I was browsing the internet for a solution, but I couldn't find an answer.
http://www.redmine.org/issues/640 offers a solution for a similar need but modifyng the same issue with js.
If this this is not the place to ask that, please let me know.

Any help is greatly appreciated.