How did you find that these 5 bytes are making the extraction possible?
If you translate the first five bytes ( 0x41 0x6F 0x53 0x43 0x2D ) of .aosc file to text it's "Aosc-1.0", this is the header ( like in zip files it says PK[] )
but the .RPA file header should be "RPA-3.0" so the first five bytes become ( 0x52 0x50 0x41 0x2D 0x33 )
But that's some shitty fix because we still need the key to decrypt the actual content and i believe the only way to get it yould be to get the build config files from the renpy project.... so yeah i don't think we can extract the game anymore... fuck
Anyways, i'll try to figure something out