This was posted in the comment section of the following video:
https://www.hahn-tech.com/thinkorswim-custom-watch-list-columns/#comment-5093
The comment was posted by Dan on October 25, 2019. Here is the full text of Dan's comment:
You can “share” your own column, then open the shared column to obtain a new column.
You can do this multiple times and just change the timeframe and the name to speed up adding columns with the exact code when you need multiple instance for different time frames. Or you can open a shared column and then change the name to something generic and just delete the column contents – then you have a fresh column.
Took me awhile to figure that out – I thought I ran out of the limited number of custom columns too. But if you share it to yourself then you yield a new custom column!
To “share” open up the script panel in the columns editing menu and then open up the colum script and click on “share” in the top right corner of the editor. Next open your shared items panel and copy the link. Finally go to your main screen to the “open shared items” menu and copy the link to rename it. Hope this helps everyone.