Not sure what your referring to by "UDF" its a standard function e.g.

Function Findnum(variable)
End Function

looking for event sub like e.g

Sub Workbook_Open()
End sub

So something to the effect of

Sub Findnum_run()
End Sub

Findnum is just an arbitrary allocation. Is that possible? I've seen a the effects of a code that does something to this effect, the sheet is locked though so unfortunately can't see how it was done.