A regular Brawl compatible Alternate Stage Loader has been released here http://forums.kc-mm.com/index.php?topic=20291.0
This makes the AFL now obsolete for loading alternate stages.Apparently not too many people know about this, so I have good news! This doubled the amount of stages I could use via Brawlex with Stage Expansion.
The Alternate Stage Loader (ASL) and Brawlex are currently incompatible. This code allows multiple stages to be loaded as "alternate" stages using a "base" stage .rel. If you are interested in the
Brawlex incompatible ASL, see
http://forums.kc-mm.com/index.php?topic=31070.0.
While ASL does not work with Brawlex 2.0.0.0, its predecessor does. Almas' Alternate File Loader (AFL) can load multiple types of files when a customizable button activator is pressed, but stages are the ones of interest for me. A full explanation of its capabilities can be found here:
http://smashboards.com/threads/the-alternate-file-loader-aka-the-clone-engine.250370/. I currently use a GameCube button activator, but I have not been able to get button activators from other controllers to work.
ASL is able to have many alternates for a stage whereas the AFL can only have one per stage. The alternate stage loaded will use the same .rel as the base stage. Only one instance of AFL will be recognized by Wiis (the first one if you have multiple), so only one function of the AFL and one button activator will be recognized. The AFL and ASL do not alter cosmetic, sfx, or strm data.
Codes for AFL (see spoiler): AFL (Core code, configured for stage loading), AF Data (Button Activator set to GameCube Y+A)
Setup: This method works using Gecko code handler. I have not tested other code handlers.
1. Insert the codes into your .gct file (check to make sure you didn't copy a code that already exists in your .gct).
2. Create these folders in you SD card (Alternate Stages will be loaded from here):
private/wii/app/RSBE/ay/stage/melee/
3. Add alternate stages to the new "melee" folder (they must have the same filename as the base stage)
How to use in game with my button activator:
1. Move your hand over a base stage (I'll use Final Destination as an example).
2. Hold down Y on a Gamecube controller
3. (Don't let go of Y) Hold down A on the same controller. Based on the Final Destination example, private/wii/app/RSBE/ay/stage/melee/STGFINAL.pac will now be loaded instead of Final Destination
Notes: This button activator is specific to the stage selection screen, so pressing the button activator elsewhere will not cause problems. If an alternate stage cannot be found (like naming your alternate Final Destination as STGFNIAL.pac), the base stage will be loaded instead. If a stage that uses a different .rel than the base stage is loaded, the game will freeze (there are some rare exceptions to this however).
This is why I have been working on achieving .rel-less stage porting. I am having progress!
Enjoy your stages everyone!
Update 3/15/2015: Bytecount typo has been corrected thanks to secretchaos1. While this did not cause any problems for my setup, it did for his.