Currently, you can only add Custom Field values to Tasks when using the multi-select toolbar.
It would be great to be able to remove a Custom Field value in bulk from all selected Tasks.
E.g., you multi-select a bunch of Tasks, choose the Custom Field picker, choose the Custom Field value, then hit a toggle saying "remove from selected Tasks".
I.e., if working with a Labels Custom Field, you could add the Label in bulk, or click to remove that Label in bulk (while leaving other Labels that are attached to those Tasks present).