[We're not still playing OP's game here, right? I'm keeping that to top-level comments only, so the rest is serious]
So if the particles are entangled, then separated by a kilometer then the state of one particle is altered, the second particle is instantaneously altered
That's not how entanglement works. A pair of entangled particles (as a system) are in a superposition of states. When you measure the state of the near particle, the superposition collapses and you instantly know the far one has the opposite state.
But you don't get to "alter" or choose the state of either particle; the outcome of the collapse is random and you just have to measure it. If you tried to impose a particular state onto the system you would sever the delicate entanglement.
Because of this, you have to encode information onto the system locally when the particles are first entangled, i.e. before you separate them. Note, the information couldn't be stored directly in the quantum states, but rather in how you arrange a set of entangled particles (a simple data structure like an array would suffice).
After separation by some distance, you observe the particle set on your side and read out the pattern of their states. As expected, that instantly tells you the remote pattern as well. However, by doing this you don't actually learn anything new that you didn't already know when the entangled particles were together locally in the first place!
Logically you cannot do all the encoding/arranging work later when the particles are already far apart, because you would lack the information to create the same arrangement on both ends of the communication (necessary to read any message, like ordered letters in a word). As you say, you would need a secondary slower-than-light communication method to share that info, and that defeats the whole point.
If it did work like you suggest where you can arbitrarily write data to your local particle set and have the entanglement transmit it remotely, then you wouldn't need a secondary verification method at all. You would know your message was received because your faraway partner would reply via the same tech in a way that only makes sense if they read it (plus maybe a few parity bits for error correction).
Unfortunately the entangled system is inherently too fragile for that scenario. Any meaningful perturbation (including measurement) collapses the necessary superposition at the heart of it. Yes that collapse can potentially reveal information, however it's limited to info that was already known in a shared local past.