I have custom fields which values are same for large continuous groups of movies, but for each one by one I have to manually edit them and choose those values after importing/scanning
Okay, now let's assume we have an "edit bar" that can save searches and consider how that might work...
First, there's there's no difference in the efficiency of entering the default values before or after the movies are added. In the more general case, it would be safer and easier to apply values after—when you can see the records it's going to be applied to. I don't know if the new tool will do this, but it would be very helpful (again, in it's general use) if it could display a drop down of the unique values currently existing in the field for the selected records. This makes it much easier for
changing values, and makes it more difficult to do so when the intent is to fill fields that should be empty. So if it worked that way, entering default values
after the movie is added (and perhaps updated) would clearly win.
Second, being able to apply default values to a set of fields all at once might be helpful if a the same set of fields/default values is commonly used,
and such sets can be saved and edited. I wonder if that's not a tall order for something not many users would need. But, more importantly, I don't think it would make all that much difference. The "edit bar" might even be more efficient, all things considered. Say a common use is like your example—you need to set four fields. The values for two of them (DVD Case # and Playlist) likely need to be updated from the last use anyway, so running those separately is no less efficient than changing the values in a saved configuration, then applying the edit. The default values for the other two may never change (I may not understand them, but it seems they would always be "true"), but that means they would be easy to pick off a drop-down list and applied. So I visualize being able to apply four separate edits using such a tool in less time than it would take to fiddle with some kind of default settings configuration, then apply the multi-edit.
Third, an equally likely scenario is that for a batch of movies the default values may not be all the same for a particular field, or some may not apply to all movies. The one-field-at-time approach is more versatile and allows such a task to be completed in whatever way is easiest for the user. That might be applying common values to all then changing those that should be different, or simply modifying the selection from field to field. This could be done with the other approach as well, but, again, would require the more cumbersome changing of the default settings for each iteration.
So while the "edit bar" may seem to be more work when there are multiple defaults to be set, I'm not convinced this is the case. Even if it is in some situations, I don't see how that can outweigh the advantages: It's easier to implement, versatile, and would be one easily understood tool that can used for a number of different purposes (e.g., MME, set default values, edit single field without having to put record in edit-mode).