P: Keywording list - deleting button

If you are nerdy enough, you could certainly do this by editing LR's SQLite database -- the ".lrcat" file. However, after taking a look at the schema, you'll probably have to be more than a little nerdy.

But if you're quite comfortable with SQL and dealing with undocumented schemas, you could sort this out. It's what I would do if I absolutely had to.

I did overrun the maximum length of the keyword list once upon a time when I imported around 100,000 images into a catalog, all of which had multiple and generally dissimilar JPEG metadata tags. By "maximum length" I mean that the list couldn't be displayed because of the 32-bit maximum size of the widget on screen, not because the list filled up. (I don't know if this has ever been fixed.) You won't fill anything in SQLite up. That's not how it's "Lite." 🙂

Also see the link below, actually meant for master vs new catalogs, but a way to manipulate keyword lists.

https://lightroomkillertips.com/exporting-importing-keyword-list/

I'm not sure why you would want to clear the list (which also deletes all keywords from the images), but as @johnrellis said, this is already possible and quite easy. No need for a special button, that you could click by mistake. If you just want to clean the list, i.e. delete those keywords that are not used in any image, then be aware that there is also a 'purge unused keywords' menu.

1. In the Keyword List, click the first keyword.

2. Shift-click the last keyword, so they are now all selected. (No need to expand parent keywords.)

3. Click the "-" button in the upper-left corner of the Keyword List panel. You'll be asked to confirm.

A button that could have someone accidentally clear their whole keyword list is something that I very much doubt would be added. It's always a balance between use and catastrophic user error, and this one would weigh heavily towards not causing the latter. 

And if you think it can't happen, people were accidentally hiding the Basic panel while right clicking on the right panel for ages.