In the Library Grid View- Select all the images to change. Make changes with "Quick Develop" Keywording, Metadata.
Try the key sequence - CTRL+A, V. All will change to monochrome. CTRL+Z to UNDO this change.
In Develop Mode- On the filmstrip Select all the images to change. Make adjustments to one, then click "Sync..." button.
You can toggle Sync to "Auto Sync" with the switch on the button. This will adjust all selected images with same edit.