Boy, what a debate here. I don't think you can hack a wordpress blog "unless" the blog owner installs your exploited code. Even according to this:
A backdoor is code that has been added to your site.
It will most likely be code not in the normal WordPress files. It could be in the theme, it could be in a plugin, it could be in the uploads directory.
It will be disguised to seem innocuous, or at least non threatening.
It will most likely involve additions to the database.
Unless the blog owner installs some code/plugin which is exploited or gives FTP user/password or gives Admin username/password to anyone, there isn't a way to hack a blog. Well, let's just forget about this debate although I'm sure many people here would love to understand what can you do to a blog but let's just talk about what you wish to know.
First of all, you are trying to make some "major" changes to the WordPress files. You wish to change the wp-config.php file which I think can be done. If you know even little bit about PHP, you would begin with looking in the index.php file in your WP blog's root. That file should have indications of where to look the config.php file. Then you can perhaps change the name at couple of places, wherever necessary and then try playing around to make things work.
Then you are asking to change wp-login.php which I believe can be done with little effort. Once again, you will have to hard code the changes in many files that link to wp-login.php file.
The best of all is renaming the wp-admin folder altogether. I guess, you are inviting trouble. May be after changing many files, you will be able to make it work with the new admin folder.
Now a few observations:
Are you sure, after doing all of this crap, your blog will be 100% secure?
Well, if someone is "so dying" to hack your blog, they will soon discover the correct admin link.
What about upgrading your blog? Whenever you will install updates from WordPress, all those changes will be gone. If you say that you won't update your blog, then you are again inviting hackers.
THINK! How much security is "enough". Hope this info helps you in some way.