Use Visual Studio code, there is no way currently to do it inside Obsidian. This will show you how to link every instance of a keyword.
Disclaimer* Make sure to make a backup of the vault before trying this. Also, this doesn’t show if you don’t want every instance of a keyword. I don’t know what to do if you still have a thousand keywords you want to add but exclude some.
If you have the free version of Visual Studio Code do the following below.
Open “New File” and insert your vault.
Go to the search tab (command + shift + f for Mac users)
Select both of the two boxes next to the search textbox (Match Whole Word, and Use Regular Expression).
Now pull up the replace option by pressing command + shift + h.
Insert the bracket version of the keyword like this into the replace textbox:
Next to the replace textbox select the replace all box. This will save changes even if you don’t have auto-save on (tested on version 1.76.2) and apply the replace on all files in the vault.
Obsidian will index and all the links will update.
“#” is excluded from the word search and up to two whitespaces are searched for to be excluded if preceded by a “#” character. This is because markdown uses these # in the title and we can’t currently have square brackets in title of markdown files for Obsidian. Negative lookbehinds in this regex won’t allow specific length from what I’ve experimented with that’s why I have it that way.