Hi Michael,
Unfortunately, you can't really extend existing features easily. If you modify the code for existing features you are forking the code and it will not be possible to upgrade without losing your changes. The only safe way to do it is to clone the feature into a completely independent copy that uses separate database tables and code.
The only other option is to convince me to include your changes so that they go into the blog feature for everyone. I'm willing to entertain the idea of integrating your work if the changes are desirable improvements and if the implementation is well done and also would need a signed contributor agreement.
I would say these are desirable improvements, so if you feel confident that you can implement them, feel free to give it a try, then send me the modified files, I will review the changes and consider integrating these improvements.
Best,
Joe