IIUC what the goal is, for one keyword you can already use *Search → More → Mark All* (or <kdb>Ctrl+Shift+M</kbd>).
For more keywords, it kind of depends on the use case; but if you cant to highlight a specific set of keywords, always the same, you can probably make a custom file type based on some non-intrusive lexer that supports keywords… that would have to be investigated for what is the best choice, but that probably could work.