simulating rc4-256 with rc4-128 OpenSSL supports rc4 with 128-bit keys and rc4 with 40-bit keys. It does not support rc4 with 256-bit keys.

My question is...  is it possible to modify the state of the pseudo-random generation algorithm (PRGA), given a 128-bit key, to match the initial state a PRGA with a 256-bit key?
NO. Without changing the API, it is not possible to coerce a 40-bit-key or 128-bit-key implementation of RC4 to behave like a 256-bit-key one, because there is no way to inject any key material in the RC4 state after initialization.

Dave_Thompson_085 has an interesting comment for OpenSSL specifics.