Is there a way to do the change in al forms at once? No, not really.
Or I need to open each form and change the property, save and close. Yes, but can do so with code instead of manually. You could research how to loop over the forms collection.
Usually when someone says they have a huge number of forms/reports in a db I imagine that many of them are just minor variations. Having a form for records that are to be view only in one situation and editable or for adding in another is not the way to go. Same for reports: not one for sales for group1 for Jan and 1 for group2 for Jan and so on. Maybe that's not the case here
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.