New sharepoint workflow action required.

I need a small action created. Basically i just need the action to allow editing of multiple items fields based on a substring. SMB - Task Name -? due date 1 - master task - 03/09/09 1.1 - sub task - 01/09/09 1.1.1 - sub sub task? - 01/09/09 1.2 - sub task? - 01/09/09 1.2.1 - sub sub task? - 01/09/09 2. - master task 05/09/09 E.G user changes the 1 master task items due date, instead of the user going through each seperate task and changing the date we need to recurse the SMB to change all the sub & sub sub tasks to thesame due date. So i poictured a workflow doing this job with an action like; E.G? With %1 Change %2 to %3? where %4? is a substring of? %5 %1 being the destination list %2 being the destination column that is being updated (due date) %3 being the current items field (due date) %4 being the destination column to match on (SMB) %5 being the current field were going to use as a substring. (SMB) Any questions?