For those of you who prefer visuals so you can be sure you don't mess up, here you go. ;)

You must have Notepad++ installed prior to the editing process. We will be dealing with encoding and decoding Base64, which is what save files in this game use to chart progress.

You can download it from here[notepad-plus-plus.org].
Once installed, double check that under "plugins" at the top, there is an option for MIME tools.

Backup the contents of your save files, found under %localappdata%\HyperLightDrifter

Decide whether or not you'd like to use an existing save (potentially dangerous) or a new save, starting from scratch (safer). If using a new save, wait for the intro to pass so you have control of your character, and then exit to the main menu.

Jump to the loading screen. Do NOT load your saves, yet. Know which save you want to modify before proceeding. Save 1 in game is save 0 in the folder, save 2 is save 1, and so forth.

Find the save file you want to turn into the alternate drifter on. Open it with Notepad++.

Highlight ALL text inside of the document. At the top of Notepad++, click on:
Plugins > MIME tools > Base64 Decode

You should now see that the text makes SOME sense now, instead of being jumbled letters and numbers. Now, search for "CH" (with quotation marks) with CTRL+F. Once you reach it, change its corresponding value from 0.000000 (Regular Drifter) to 1.000000 (DLC Alternate Drifter). If you want (though I don't recommend it), you can change the value to 33 or 5 to try out Beta versions of the alt drifter, though they are VERY buggy.

After save modification, highlight all text. Go to Plugins > MIME Tools > Base64 Encode

You should see your save file contents return to "normal." Save the file, close out of Notepad++, and load the save you modified in-game. It should look perfectly normal, but upon loading in, you'll immediately see otherwise. :)

NOTES:
Upon closing the game and opening the loading screen, you will see something like this:


Because you don't actually OWN the DLC for the game that was available ONLY to kickstarter backers who paid $75 for the package, you don't have a way of loading back in conveniently.

To fix this, you will have to follow the guide again, but replace the "CH" value of 1 back to 0. After re-encoding and launching the game again, you'll have a regular drifter on the loading screen. Then you just follow the guide to re-modify the save to load the alternate drifter, and you can resume the fun. :)

DISCLAIMERS:
I am NOT responsible for the safety of your save files. If you mess up, tough luck. There's a reason I put backing up your saves as a step.

This guide was made so that people who don't have the DLC can access it. I know this will upset some backers, but c'mon. It's been like 7 months, guys. We've waited for quite a while, now. XD

When the DLC is released, please purchase to support Heart Machine. Those guys deserve it.