It’s not going to be permanent, but there is something else you could consider using, for something specific to this. I work very similarly to you, I have a series of tokens or keywords that I type into the text where I want to fix things, or come back later and read again with a fresh perspective. For these I use inline annotations, for three reasons:[1]
- Most importantly, by default they don’t export. So I don’t have to worry about them ever ending up in the output.
- They come in colours! You can colour code, they stand out visually, etc.
- The
Edit ▸ Find ▸ Find by Formattingtool can trawl annotations specifically by colour, and for text within annotations. So the colour coding isn’t just visual.
As it’s somewhat tangential to the concept of automatically highlighting words based on search matching, here is a thread that specialises more in marking text with tags, that starts off with a curated list of links to other discussions. Bit of a network there. 
§18.2.1, Inline Annotations, in the user manual PDF. ↩︎