Access forms don't have the nice MouseOver and MouseOff event that web pages do.
They have MouseMove instead.  The difference (and problem) is that it fires
constantly, once for every pixel change of the mouse while you are over the
control, not just once moving over the control.

Since it is rare that one would actually want their code to fire continuously
like that you have to put hacks in to try to limit the code to running only once
until the mouse cursor leaves the control while still running again should the
cursor return.  In my experience this is difficult to achieve without a lot of
problems and/or screen flicker.

Stephen Lebans (I think) has an advanced mouse-over example that you might want
to look at for ideas.

There is no reason you couldn't use a single function for all the text boxes.
Just pass the name of the control to the function and use it to determine
what text you need:

Private Function SetText(strCtlName As String) As Boolean
Dim ctl As Control
Dim strText as String

   Set ctl = Me.Controls(strCtlName)
   
   strText = 'Do the logic to select the text

   ctl.ControlTipText = strText
End Function