RoyUK, thanks for your comments.

Changing the \ to a / didn't make any difference to the way the code ran, but I still cannot make the code update remote and external references automatically by adding 3 to the end of the line. As soon as I do add the 3, the code does not compile.

This is the start of the code I am trying to update to stop the appearance of the "Update - Don't Update" windows.

Sub PopulateDataRisk(NumberOfLines As Integer, AssessmentPath As String, FileListStart As Range)

Set RegisterWorkbook = ThisWorkbook

For i = 0 To NumberOfLines - 1
Set TempWorkbook = Workbooks.Open(AssessmentPath & "/" & FileListStart.Offset(i, 0))

Dim DataArray(18)

With TempWorkbook
    DataArray(0) = Range("LOF_Ref")