Misusing your site's HTML tags is not a wise long-term strategy. You will run the risk of irritating the good folks at the search engines who have total and complete control over their index and can ban your site from their index without even telling you of your violation, In fact, the search engines may make a new rule tomorrow based on some technique you have just invented and implemented, decide that you have offended them or broken this new rule and ban your site from their index. They are the judge, jury, and executioner. Why "push the envelope" and test their patience?
Building relevant, keyword-rich content where the targeted keywords are contained in the important HTML element is a good long-term strategy. If you place keywords in the body copy, in the site's Title and META tag, and in activated links, and then work to increase the number of links from external sources to your website, you will attain rankings.
I will caution you against what I call working in a "false economy." You may think you are saving time, but if you apply an overly aggressive tactic and the engines find out, you will spend more time undoing the damage such as changing all the pages you have built that contain the offending HTML code and fixing it, writing apology letters to the search engines, and sending emails to them, hoping to learn if your site is banned or not. Here today, spam tomorrow. You should do your level best to only espouse the techniques that work and will remain valuable in the long run.
Much success can be achieved by working with above-the-board, visible HTML. There may be a slight benefit to edited your site's META tags or editing the Title tag and see what happens in one search engine or another. But tweaking HTML tags that were never intended for metadata so that they can contain your keywords is, in the long run, folly. Search engines change their ranking algorithms frequently, and using "tricks" are not likely to produce a high ranking for any valuable length of time. Most search engines look askance at any HTML you place on your webpage that is intended only to "trick" their algorithm. Search engines have no recourse against people who use unconventional HTML code in their website other than target users for a penalty or simply disable them.
You should invest you time in making sure that your HTML documents contain the targeted keywords in several different places and that the metadata is accurate and complete. Compare your keyword frequency, prominence, and weight with higher-ranking documents. Compare your link popularity with other Web documents and work to improve it. This is all you need to increase your ranking in search engines