That was quite fun ....This code worked fine on 3 test files i selected.
I have commented the code to explain - I assumed that the range A4:A10 was text that needed replacing by B4:B10 - just expand the ranges in the master file if you need to adding extra words/phrases...
Dim ws As Worksheet, wb As Workbook
Dim fList As Variant, I As Integer
Dim rng1 As Range
Dim cel As Range
Dim strMyChar As String, strMyReplace As String
Set rng1 = .[A4:A10]
fList = Application.GetOpenFilename(MultiSelect:=True)
If TypeName(fList) = "Boolean" Then
MsgBox "No files selected. Activity halted."
For I = 1 To UBound(fList)
Set wb = Workbooks.Open(fList(I), False)
For Each ws In wb.Worksheets
For Each cel In rng1.Cells
strMyChar = cel.Value
strMyReplace = cel.Offset(0, 1).Value
.Replace What:=strMyChar, Replacement:=strMyReplace, _