I have a custom wp-login.php – how do I turn it into a plugin?

First off, I’m not a developer. I did programming many moons ago so I understand it and can hack my way around if I need to, but it isn’t my cup of tea.

Anyway, I have a client whom I had hacked a new wp-login.php file that included some special text callouts, hooks into their e-mail manager for lead capture (for registering folks), and some minor cosmetic changes. I did all this several iterations of WP ago and every single time they decide to upgrade, I have to go in and make all the changes again. Not an efficient way of doing things, I realize this.

To help, I did manage to put 99% of the changes in external files that are called with includes in the wp-login.php file, but I have to go through a DIF the files (old/new) to find where to place them every single time and to make any other modifications needed due to code changes in the releases – which lucky for me have been almost none in the areas I modify.

So I have this custom login file – what is the best or easiest way to call this INSTEAD of the default file for login/registering? If it’s creating a plugin, how the heck do I completely negate the default login in favor of the new one?

And while we’re discussing this, I did think of a work around, but it probably isn’t the smart way to do it. I was thinking I could just redirect the wp-login.php file to my new file and leave it at that. But something tells me that would cause some yet unforeseen issues.

Please let me know what you think and try to keep it fairly straightforward terms. Oh and I did look over the docs regarding hooks and actions and plugins…. that didn’t help since what I want to do is completely override the default file with a new one.

Anyways, thanks in advance.