Honestly, you should see any real changes with your current rankings. Title tags are one of many factors that determine Google search results; the changes will most likely have an impact on the additional keywords you've entered. However, if you broke any keywords up and replaced their order there is a slight chance of a negative effect.
it depends on you how u change the title of web page. If u do like title: ab after change title: abc Not negative effect in rankings If u change into title : acb It effect and requied seo for that keyword.
Changes to <title> can definitely change your rankings, especially for keyword phrases with very low competition where you can get ranked based on on-page factors alone. <title> is the most important on-page ranking factor for most engines. Be careful not to lose sight of the focus of your page when optimizing title tags.