Does anyone know whether changing your title tag after the site has been up for a while will negatively affect SEO?
In my opinion it could help or harm. Depends on how you change it. If you change it for the better, i.e. better keywords or word arrangement it will help.
That depends, are you ranking for the keywords in the title tag and do you want to keep those rankings. As long as the relevant KWs stay in the title tag you wont have any issues.
I have a site that ranked no 4 on Google for about 270,000,000. I changed the title tag and the keyword tag a little bit, and it dropped compleately out of sight It's slowly climbing again, and are now about 200. If You have good rankings, I would be careful, if not, it probably would not do much harm.
I'm ranking well for an fairly uncompetitive term, but I wanted to try changing it to a very competitive term to see if I can make progress with it.
It depends on what title you currently have for your site. If you are replacing it with better keywords, ofcourse it will help with SEO.
What if I keep the same title tag I have, but tack on a very competitive term at the end? Would only adding to the title affect seo?
It can help if you do it right, and hurt if you do it wrong. Use keywords in your title tag at the beginning, and if you're including company name or site name for branding, do it at the end. Try to max at 10-12 words. You need to balance making it work both for search engines and viewers. The title should be catchy and appeal to people. Think think of it as a free "ad" (think adwords). The title is the headline, and the description tag is the ad copy. It needs to prompt the viewer to click on it, since it's useless to rank #1 if no one clicks.
^^ This have been my experience as well. ^^ If your site is already ranking well with the existing tags, then I would leave it intact. I would create a new page (keyword rich) with new tags and link to the page internally.
try and get a different page to rank for that keyword........getting a page ranked for more than 2 terms can be difficult
It will help you if u can hit the right keywords. But if you over do it it might harm you. If are already ranked well in the SE...then don't do it.
IF you have confidence that changing your title tag will help you inproved your rankings, then go for it.