I'm pretty sure you can change all the settings of your game page at any time.
Ok, so that was the problem indeed: the web version has been uploaded and can be activated... even if at the moment there are several bug to fix: seems that just making a WebGL build is not enough to make work a generic build of Unity.
Seems that in particular it's problematic to handle the saving system which doesn't look at the original path anymore, btw it's a JSON the save files. For the moment i'll remove the web version and try to fix it testing on Unity