It needs to be more than 'a little extra'. It needs to advance the state of the art. It needs to have a new idea in it. It can't just be a better implementation of something we already know how to do.

There is no standardisation. The level you are assessed against is set by your examiner.

Don't focus on the thesis or the software - those are just ways to express your novel idea, which is what is being assessed.

But yes you can do whatever you want, as long as you have a good idea and can show it works.