For our operation, we do not need to consider a TEMPO for a nominated EDTO Alternate Airport, if it is less than PROB 40. If it is PROB 40, we then need to consult if it introduces a requirement with WX forecast to be below company published EDTO minima.
Once dispatched, we can disregard TEMPO and must prior to the EDTO Entry Point (EEP), verify that forecast for EDTO-Alternates are above Landing Minima for the period in question (Early Arrival to Late Arrival), for each individual nominated EDTO Alternate.
Once we have hit EEP, all bets are off - we may continue to destination, even if EDTO-Alternates become or are forecast to drop below landing minima.
You must however, check your own company's requirements. CASA may vary this upon request from each individual operator.
Hope that helps - RJ