How to merge items using keyword A with keyword B

I’d like to merge keywords because I added my on the fly and ended up with duplicates.

I have moved your reply to a new topic, since the original post was essentially asking for keywords to be removed from the software entirely, and turned into another kind of feature.

It sounds to me more like you do like Keywords as they are, but have ended up with some typos or other close combinations, and want to bring these variants into one unified keyword. Let me know if that is not accurate.

But if so, the way to do this is very easy:

  1. Open the Project ▸ Project Keywords panel and select the keyword you wish to remove, but don’t do that just yet.

  2. In the lower right corner click the magnifying glass icon to search for this keyword project-wide.

  3. The binder sidebar will change to showing only those items that are using this keyword. In the sidebar, click one and press ⌘A (Ctrl+A) to select them all.

  4. Back in the Keywords panel, right-click on the keyword you want to merge to, and select the option to apply this keyword to the selection in the sidebar.

    I would suggest clicking through a few of these items one by one, with the Inspector open, so you can double-check that they all now have both keywords assigned.

  5. With that done, delete the keyword you don’t want from the Project Keywords panel. You will be warned about this keyword being in use. That is fine because you’ve already assigned those items using it to the other keyword as well.