Public Function testAc() As String
On Error Resume Next
Dim frm As Access.Form
Dim ctl As Access.Control
Dim s As String
    For Each frm In Forms
        For Each ctl In frm.Controls
            s = ctl.Properties("defaultvalue")
            If err <>  0  Then
                s = ""
                err.Clear
            End If
            If s = "=TestAc()" Then
               testAc = ctl.Properties("Name") 'controlsource и т.п.
               err.Clear
            End If
        Next ctl
    Next frm
End Function

Public Function testAc() As String
On Error Resume Next
Dim frm As Access.Form
Dim ctl As Access.Control
Dim s As String
    For Each frm In Forms
        For Each ctl In frm.Controls
            s = ctl.Properties("defaultvalue")
            If err <>  0  Then
                s = ""
                err.Clear
            End If
            If s = "=TestAc()" Then 's = "TestAc()" и т.п.
               testAc = ctl.Properties("Name") 'выставляем  1 -е
               ctl.Properties("defaultvalue") = ctl.Properties("Name")
               'снимаем с обработки в циклах
               err.Clear
            End If
        Next ctl
    Next frm
End Function