No. Noooooo. In the words of J Allen Brack, "Nooooo. You do not want that, to do that. You think you do, but you don't."
I am a person with the technical knowledge to more or less do what you are asking. During Reforged Beta I developed a computer program to sort of "unwind" the Reforged installation's assets and rewrite it as a 1.26 mod. I was simply curious, as a human, about the possibility and about the technology. I also wanted to prove to someone who was asking me... that it was a bad idea. The conversion process, since it needed to process 30 GB, was very slow until I parallelized it and got it running on all cores of my 12 core CPU simultaneously. As I recall, this caused my computer to make a loud noise as it ran near full capacity for about 30 minutes.
When this was complete I beheld the most stupid and terrible Patch 1.26 mod in existence. It had its own 3d HD Menu background back in the beta before they switched to the HTML Reforged UI. And so yes, these files were "compatible" with 1.26 after the conversion, except that they weren't. We hit the limit on the mesh data and 3D files would graphically explode. The menu was an epilepsy danger. I recorded about 30 seconds of gameplay on this mod in a video titled "This is why we can't have nice things" to prove to whoever it was that had asked me to do this that they do not actually want to do it.
After about 30 seconds something happened that surpasses my understanding. The game went into a "black state" due to memory corruption probably due to the exploded models and to be honest I forget if it crashed after this or if I closed the game for fear of damaging my computer.
I quoted you because this claim you make, "since it's the same game, same model structure" is, in my opinion, a technologically uninformed claim. If you think about how you can convert a PNG image to a GIF, but you cannot convert a GIF to a PNG because the PNG has no way to store animations, it is similar to this. A PNG can store an image, and a GIF can store an image that might be animated. In the same way, the Reforged MDX format can store the 1.26 MDX models as well as the Reforged HD models. But the 1.26 MDX format cannot store the Reforged HD models.
Even my backwards translation program that I created for the sake of example was throwing away substantial portions of the art that cannot be stored in the old format. Although it would be possible to create further iteration on the stupid project I created, it would from my standpoint be a waste of time.
You can see in the video the footmen do not animate, for example. I could fix that and then reconvert the whole game again. I did not back then know that Reforged MDX allows out of order sequences when Legacy MDX does not, and so my converter did not reorder sequences, which would have been necessary. In addition, I think that the model explosion may have been due to creating more than 256 vertex groups which would overflow the 8 bit unsigned ID system, although I forget. If that is true, then we could update the converter to split the model into more pieces that each individually do not overflow the 8 bit unsigned ID system.
I was also once criticized by someone who said that my direct use of diffuse textures instead of baking all Reforged textures together into a composite texture for the old diffuse-only system was also my own fault and not proof that the conversion is impossible. Sure, but, I do not care. Even if we assume a static daytime light and bake based on this, models who use the same texture in two places might now need two textures... we're talking about driving up the complexity of the backport script
a lot. But I suppose if you did then you could also bring back teamcolor in most cases when it was not used side-by-side with alpha (which while legal on HD is literally impossible in SD without an artist splitting the model into bits and choosing different materials on different bits).
So you solve all that and then you realize that reading from pkb or fafx to produce something compatible with 1.26 is harder than reading from protected maps, and so you lose all particles and portrait mouth movements.
To be honest this is just a stupid project idea that is not worth it at all once you understand the technicalities. If you want to play Reforged, then just buy Reforged... seriously.
Edit: Although I have no intention of supporting this nonsense, while I was testing the above video I wanted a way to convert a single model file at a time rather that only being able to convert the whole game at a time. This was faster to test with to find bugs. I had been testing on the Paladin prior to converting the whole game, which is how his model in the video is the only one that doesnt look like
completely broken garbage. During my test I added a button for "HD -> SD" conversion in Retera Model Studio. I meant to delete this button before publishing the next version of Retera Model Studio, but I forgot. Later I found ignorant people were actually trying to use it.
And one time I heard a rumor that some ignorant people might have spent a very long time clicking that button over and over on every model in Reforged to build a mod. Maybe it was Argentina, I forget. You should not click that button over and over. Side-by-side with it I developed a way to convert the entire game which I never published. If you were going to be stupid, at least do it in an automated way so you only spend 30 minutes of your life learning your lesson...
