Translate BR variable "User ID" to dimension or smart list member?

Summary:

Can I translate a BR variable using the User Name default value into a dimension member or Smart List value?

Content (please ensure you mask any confidential information):

Users log in using their numeric ID, which is their Kronos ID, a five- or six-digit integer. In CalcMgr I have set up a replacement variable, type String As Number, to "Use System Defaults" value User Name. This successfully returns their User ID, which I can set a text member equal to without issue, and we can use this in a BR to set text members like "Created By", "Approved By", etc. to that user's Kronos ID.