I have created a test and then generated a code of that test. I have changed that code (minor changes). Now Can I import that code again to modify my test?
You cannot record on uploaded coded tests.
You can execute them and can add them to jobs along with recorded tests, however you will not be able to open them the same way as a recorded test and edit each step individually through the UI.
You can however, keep editing and working on your code, and update your uploaded coded test package when needed.
This of course, applies to code generated from your recorded test cases if you are uploading a .jar or .dll file/zip.
If you want to import the generated code back into the platform after making your small changes, generate the .jar/.dll for that test and when creating a new test select the coded test option and then select your file:
Thanks @david.goichman. I am digging it in detail and then will get back to you if needed.