Building a String to Save as a Data

How can I build a string consisting of a combination of text and existing data, and then store this new string as a data? For instance, we have a number of groups that are formatted like this: WFG_“BU”_SHIPPERS where the “BU” can vary depending on Business Unit. The initiator would select the Business Unit (such as ABC) and we store that value. Later on I would use GETUSERSFROMDIR and use this value to piece together the full list of users in the group (WFGABCSHIPPERS).

You can create a hidden text field, and on the onselectindexchange of the Business Unit drop down, build your text of the hidden field(you will need to wrote code behind). Then in mapping, map the hidden field to a process data (say GROUPNAME) and use that process data in the GETUSERSFROMDIR