I discovered a trick by accident - how to copy B&W settings only from one image to another. 1) create a clone variant of the image you want to make B&W. 2) copy the settings from your source B&W who's B&W settings you want to copy. 3) paste these settings on the clone variant you created. yes it will overwrite your existing adjustments. 4) copy the adjustments from the variant you cloned in step 1. 5) paste the settings onto the cloned variant. Steps 4 and 5 put back the adjustments you already made to the image and only leave the B&W settings you add to the source B&W image. Not perfect but a good start when you have lots of images taken under the same setup like a studio senior portrait session, etc.
I go live every Tuesday 10am or Wednesday 9pm Pacific for a show of random chattering and meandering tech. Get any lingering questions you have answered!