Ok thank you very much!
I tried to find it, but the place of the offset of the frames for battle UI is a bit difficult to find for me.
I'm not sure if it is even possible, because making a trace log of FFNx it seems to load btl_win at the beginning of the game, and then, when the game enters in battle scene, it seems to load something... different.
This is when the game loads:
[00000099] TRACE: Renderer::createTexture: 60 => 51594840x51594844 from filename C:\Games\Final Fantasy VII/mods/textures/menu/btl_win_a_l_00.dds
[00000099] TRACE: Using texture: C:\Games\Final Fantasy VII/mods/textures/menu/btl_win_a_l_00.dds
[00000099] TRACE: Created external texture: 60 from C:\Games\Final Fantasy VII/mods/textures/menu/btl_win_a_l_00.dds
This is when battle begins:
[00001111] TRACE: gl_defer_sorted_draw: call with primitivetype: 4 - vertextype: 3 - vertexcount: 32 - count: 48 - clip: 1 - mipmap: 1
[00001111] TRACE: gl_defer_sorted_draw: texture_set true for texture menu/btl_win_c_l0
[00001111] TRACE: gl_defer_sorted_draw: return true
So it does (or FFNx is doing) something different. I searched this to use in 7H a Runtime Var telling when it enters in battle use a different btl_win_c_l, but I have not good results with this.
Another thing I found is to change the colors/alpha of the background of the Help/Status boxes:
This is the code:
http://BATTLE MENU
# Help Support -Middle- & Message -Up- Windows Top Left/Right/Top/Bottom Colors
#.text:006D4EF7 mov ecx, dword_91EFC8
6D4EF7 = B9 00 00 00 7F 90
#.text:006D4F7F mov ecx, dword_91EFCC
6D4F7F = B9 00 00 00 7F 90
#.text:006D5007 mov ecx, dword_91EFD0
6D5007 = B9 00 00 00 7F 90
#.text:006D50A2 mov edx, dword_91EFD4
6D50A2 = BA 00 00 00 7F 90
Altough I researched this also for the rest of Battle UI (searched for 0x91EFC8), the only place that I could modify this with any result, it changed only the background for the rest of UI, even the menu UI, leaving it in black color, of course.
So, if we could find a method to change btl_win_cl and background colors for Battle UI, we could have a different Battle UI from Menu UI.