You're thinking about creating a whole new back story, but one that actually makes sense? That would be sweet! The problem, though, is that it's impossible to spot all the plot holes by yourself - even if you wrote it - so you would have to show the script to as many people as possible. And you should probably start with writing an outline or something like that, like a rough draft with little to no dialogue - and see what other people think about it. Writing a script - that alone will be very time consuming. I say, 1st you write it and don't even think about how you gonna draw it.