I'm sorry that the add-on didn't meet your use-case. I'd like to share a couple possible workarounds though. Instead of highlighting the "filtered" words, you can change the filter mode to "Off" (disabled/summary only). Then, open the page to the lyrics for a song, and click on the add-on's icon to bring up the popup menu which will list what words (and how many) were found. That will leave the page unchanged, but will still give you a summary of what was found.

Alternatively, you could try switching to the censor mode, choose to keep the first and last characters of filtered words, and then change the censor character to one of the colored blocks.

If neither of those work for you, I'd also be happy to discuss adding a feature that could help you if you are interested. Unfortunately directly highlighting text can get tricky with how many different variations between websites there are, but its something I could look into more and see what could be done.