No it is not part of b2evolution to have "global" settings. Yes you could change the default values for a new blog probably possibly by going to your database via phpmyadmin and changing what it says for the default value. Yes it might not work because the files might also set them to whatever it likes. Sorry, but I don't know what files you would want to change.

I suggest starting with changing the default values in your blogs table in your database and see how many of them actually change when you create a new blog. Then, if you tell us what happened, you will be the expert and we will all be a little bit smarter.

And hey welcome to the forums!