|There are many, many ways to accomplish this "now" request.|
If the first part of the filename that you are looking for is in a cell in the worksheet, the macro could read that cell and build the filename. For example if A1 contained the word Sales, this should work:
MyFileName = Range("A1") & "_" & MyMonth & MyDay
Or you could have VBA grab the first part of the actual filename, up to the underscore, as follows:
MyFileName = Left(ActiveWorkbook.Name, WorksheetFunction.Find("_", ActiveWorkbook.Name)) & MyMonth & MyDay
Or you could have VBA present an InputBox asking the user for the first part of the filename, but that would take away some of the automation.
None of this would extend the filename like you were afraid would happen.