Set All Texture maps to Max 1024x1024?
Is this somehow possible?
You can edit values of multiple textures at the same time, if all shall have the same values. Select multiple textures, then right click on them, then go to Asset action, then you will see a new entry called “Bulk Edit via Property matrix”. Click that and wait until it´s loaded. Then you just have to find your entry in the right category and change it to an uniform value. Works with meshes too, but loading times might increase considerably, if they are big, so give it some time for loading 
Looks like this:
