The SC4 file format is essentially identical to the SV4 file format. There are some minor differences. There is one major difference introduced with the first expansion pack. An additional encryption method was added. This was apparently intended to impede independent developers from creating a scenario editor. It serves no programmatic purpose that I can tell. Here is a description of the additional processing needed to inspect SC4 files that are intended for the expansion pack(s).
1) Load the file into memory and perform the usual RLE decoding.
2) perform an "XOR with 9C" on every byte from 60018 to 1F8353.
3) perform a "rotate-right-by-3" on the second byte and then a "rotate-left-by-9" on every DWORD from 60018 to 1F8350
To go from SV4 to SC4, reverse the above process. (untested) Note: remember the checksum values.
Here are the scenario assignments.