File Save Macro as Cell content
 

I currently open a workbook that goes to cell A1 which contains a filename
with required filenaming conventions(REPORT NAME_DATE_PG#_MST#). I want the
user to be able to edit the cell if the content equals "REPORT
NAME_DATE_PG#_MST#". Once they edit the cell and finish populating the
worksheet they will close the workbook with the current content on cell A1 as
the new filename.xls(Sudbury_012907_PG1_MST003). Also once they have changed
the A1 cell content it should lock and not be able be changed again no matter
how many times they open it.