If you rank for a phrase that you don't want to rank for, there's not much you can do other than make sure that your content does not include this phrase. Adjusting the description meta-tag and the title element to give more information about what you are really writing about can be helpful as well, although this may not affect your ranking for that phrase. Adding a "not" qualifier won't really help to change the ranking, but it might help users who are looking for something particular.

One trick you could try is to replace individual letters with alternate glyphs that look very similar. For instance, you could replace a lower case "L" with the number "1? (or use cyrillic characters that look very similar, eg "e"/"?", "r"/"?", "i"/"?", etc.). While this would make it harder for us to understand your content (say if someone wanted to use Google Translate to read it in their own language), it would likely also prevent your content from ranking for those words.