It is about 2 month since I am working for my site, now I want to change some of my keywords. Does it harmful for ranking?
It's not harmful- trust me. Just change it and that's it. If you were building your links right and not giving f*ck about anchor text and optimizing your website in that way, then there is no need to be stressed about it. Relax, everything will be fine.
Truely you should not focus too much on specific keywords only, because it will lead you to penalization, money terms should not take more than 5% each, I don`t know how much of keywords you are targetting for but if not many I advice you to increase the amount of keyphrases to as many as possible including LSI, of course it`s hard to optimize website for all of them, but LSI and generic, also URL and brand name should be biggest part of your anchor profile.
It is not harmful to change keywords. Even you will have to do same promotion work again for new keywords. This time, you should choose right keywords for your website otherwise changing keywords will not be helpful for you.
Before you finalize the new keywords or change them, make sure to check you backlink profile. It might be the case that some of your keywords might be over optimized. You must be aware of this before planning the keywords.
No change at all, you can always build backlinks on a different keyword, just be sure to also optimize your content!!
Changing "keywords" is the wrong approach. Change the "content" in order to change the overall "focus".