I am new at programming so I can't help in terms of correcting your code but I can see one area of trouble. See below.

Sub Over50()
Dim WeekNumber As Integer
Dim WeekChanged As Interger

WeekNumber = Range(E5)
WeekChanged = 50

If WeekNumber > 50 Then 'Check if WeekNumber is > then 50
WeekNumber=WeekChanged 'Change Cell E5 to equal 50
MsgBox "Too Many Weeks. This Number Will remain 50" 'Show message box
End If
End Sub

You haven't included in your IF statement a means for WeekNumber to be changed to 50. If you do not include WeekNumber = WeekChanged all that will occur is WeekNumber will retain its state, will stay > 50 and your messagebox will show but no actual change will occur.

I don't know if WeekNumber=WeekChanged is the correct VB code or if the Integer WeekChanged is declared correctly.

I will keep working on this and will post if I get any results.