Please consider implementing the use case you are looking for using a LivePage.
What the wiki page does:
It shows the Documents of the actual project and allows you to chose a prefix and step for each Document's Work Items. Then it calculates a specific Identifier based on the steps which can be written in a custom field of each Work Item. The steps are incremented at intervals of the chosen steps.
For example, if you type in Prefix: AAA Step:5, the Work Items in the Document will get a new custom field labeled Identifier with the value AAA-5, AAA-10, AAA-15, and so on. You can find further information after downloading the plugin in the file 'README.txt'.
Version 1.0.1 | Version 1.0.2:
Fixed the 'Preview' view which in some cases resulted in a NumberFormatException.
Edited a misleading infobox.