General Ledger Department Number by Attorney

Neither the Group assignment on the Timekeeper record nor the Department assignment on the Matter record have anything to do with the GL.  If you are talking about expense accounts set up for attorney Departments, if you moved the attorney and wanted the GL detail to be split between the two Departments, you would have to add a second GL account for the "new" Department. If you want all historical expenses to go with him, you would just change the account number of the existing account.