Вот два примера
'-----------------------------------------------
Dim AR(5) As Long
Call TestArray(1, AR())

Public Function TestArray(ByVal P As Long, byref AR() As Long)
MsgBox UBound(AR)
End Function
'-----------------------------------------------

'-----------------------------------------------
Dim AR() As Long
Call TestArray(1, AR())
Public Function TestArray(ByVal P As Long, ByRef AR() As Long)
ReDim AR(P)
MsgBox UBound(AR)
End Function
'-----------------------------------------------