It will be possible to achieve if you create 2 custom fields and then concatenate them via Work Flow Rule.
We have an app in place called Project Numbering: (please see more information there: http://www.clarizen.com/appsmarketplace/item/Project-Numbering.html). You can refer to this app and its logic while creating your workflow rule on a Request Entity.
If you would like further assistance, since customization requests are out of scope via forum and we want to make sure we provide best practice advice that will meet your requirements and help you achieve your business goals with Clarizen, please let me suggest the following:
If you purchased hours with you Customer Success Manager, please reach out to him/her and he/she will be able to work with you on customizations.
You may also choose attend our Advanced Q&A webinars, there are great resources for free consulting with our Customer Success Managers and visual answers to your questions > http://www.clarizen.com/live-demo.html#second.