I have completed my 2-years of B.Tech civil engineering in Hyderabad. Can I apply for another 2 years of B.Tech through distance education?

You can't apply for any other institute between your 4 years B.Tech regular course. However, you can take transfer to another campus branch of same university or college.

No, generally it is not possible. Once you get admission in regular system or through distance mode it got registered for that batch. But, you may contact to your college administration, if they have any rule they will tell you.