Hi,
I had another look at the BGL opcodes, and I don't think you have a problem with the amount of textures yet. That is only after about 800 texture entries if I calculated it right.
You only have 270 textures so that should be fine (the night texture needs to be defined for every seasons, since it is a subtexture type).
So I had a look at the code and it seems the problem is with the IFIN1 command. This command can only jump over 65536 bytes of code, I think you have too many polygons for this command to jump over.
To get around that you would need to restructure the entire code. Maybe it is easier than to export as two files.
Btw, I am working on tool support for ground polygons, so that in the future ASM tweaking to get seasons is no longer needed.