Dreams do come true
Thanks to
@toxic9
https://gbatemp.net/threads/super-mario-land-dx-mod.592360/
Still a bit buggy but I already like it better than the modified sprites.
I did something similar way back when SML DX recently released.
I created the Mario sprite to be similar to the original SML, but with the color scheme of SMB on NES.
The problem Toxic has with the jumping frames is due to the sprite Toruzz made being separated into two 8x8 sprites, and each one having a unique palette.
The bottom 8x8 sprite uses white, red and blue for the colors, while the top 8x8 sprite uses beige, red and blue, and given how Toruzz's new sprites are taller than the original SML sprites, when changing the sprites back to the original size, you end up with Mario's head having to fit into the bottom 8x8 sprite, hence the white face on some frames.
One way I fixed this was by giving both the top and bottom sprites the same palette, but the downside of this is that certain items that share the bottom 8x8 sprite palette also get modified. Another way is to still keep both body and head separate, and move the head sprite lower in a tile editor.
An easier way to do this would be to give Mario's bottom 8x8 sprite the same palette as the top one through sprite attributes, I'm sure that should be easy to do, but sadly not something I have the expertise to do. Perhaps Toruzz himself could give an insight as to where to look for this.
However, it's better to wait it out already, Toruzz is close to finishing 2.0 of SML DX, and he will be releasing a method of switching back to the original sprites.