Someone told me all I had to do was remove the Master Chief's data in the masterchief folder of a10 and replace with the corresponding data for my custom biped in Halo Editing Kit Plus.

Is that all I have to do? If so, I must be doing something wrong because every time I try to run the a10 I'm working on, Halo crashes and I'm forced to close and reopen HEK+.

This someone is wrong. Read the how to make/edit maps thread.

Thanks. Thing is, I can't find what I'm looking for there....

You have to:
1. Start Guerilla
2. Open globals.globals which will be in your halo custom edition\tags\globals\(globals.globals)
3. Scroll down until you see the "Player Information" section
4. Change the biped directory there to the one you want
5. Compile Your .Scenario into a Map with Tool
6. Play the map
7. Done :)
P.S.
A little bit above the Player Information section in Guerilla is the "Multiplayer Information," that's where you would change the player's biped for it to show up in a multiplayer map.

Exactly what I needed! Thank you very much!

Still need to tweak what weapons she can and can't pick up, but I think I can do that on my own.

HIRALIS, it wasn't a grammar mistake.

I was hoping to keep this a bit of a secret, but I am currently working on combining the Campaign maps with Samus Aran's data from the Metroid Online project.

You could call it Metroid Prime: Combat Evolved. Progress is extremely slow, but I think I should have a decent beta a10.map file by March at the earliest.

Unfortunately, since I am (technically) on my own for this project, I doubt I will make any serious changes to the Campaign mode. That includes making Zero Suit Samus.

Unless I can assemble my own team for Metroid Prime: Combat Evolved, the first beta will only see Samus replacing Master Chief, the Power Beam and Missile Launcher as the only available weapons (with Missile count topping out at 10) and four times the health but removing the energy shields.

At least, that's what I currently have planned, anyway.

That was the 2nd helpful thing I wrote :D I'm on a roll :D lol