I don't know if this is the most macro-friendly (streamlined) way to do it, but this is how I do it using standard Lightroom Classic keyboard commands:
Lightroom Classic has a convenient feature in the Library module: It keeps the current field active if you switch images with the keyboard. So as long as you do that, you can simply paste all keywords that are on the clipboard and then use the keyboard to go to the next image and paste again. It works like this:
- On the first image, click in the larger keyword field in the Keywording panel. (To do this with keyboard shortcuts on the Mac, press Command-K to get the small entry field, then press Shift-Tab to back up to the bigger field above it that contains keywords already applied to the image.)
- Type the keywords for the image, separated by commas.
- Press Command-A to select all the keywords in the field.
- Press Command-Right Arrow to go to the next image. This is where it's great that Lightroom Classic keeps the current field active, because now you can just…
- Press Command-V to paste all of the copied keywords into the current image's keyword field.
If there are more images to do, this is where it goes fast. It's simply:
- Press Command-Right Arrow.
- Press Command-V.
- Repeat for as many images as needed.
When going from image to image, another nice thing Lightroom Classic does is that there's no need to press Enter or Return in the big field; the keywords are committed as soon as you leave the image. You don't want to press Enter or Return anyway, because that would commit the keywords but also exit the field. (You do have to press Enter or Return to commit entered text in the smaller keyword entry field, which is why the smaller field won't work for this.)
If you have to paste the same keywords into a large number of images (like 200), it's probably faster to select them all at once with the mouse, click in the big keyword field, and paste them all in that way, compared to pressing Command-Right Arrow 200 times. Or, if you're building a macro that lets you enter options, maybe you could have the macro ask how many times you need it to repeat, and if you know there are 200 subsequent images that need the same keywords, you could enter that number.