Unfortunately no, Apple has usage limits on iMessage / SMS relaying. Many people hack around this, SendBlue.co being the only long running service, but it's full of the graveyard of folks trying to do this.
What does this mean in practice? I leave my Messages app on my laptop open all day and correspond entirely through it with family. Since I'm typing I send messages rapidly at volume. I've never once hit a limit. Think hundreds of responses a day.
If an app running on my machine has subclassed the Messages app and is reading strings and sending hit strokes to the (Send) button on my behalf, how can Apple possibly rate limit this?
It's probably like those email providers that allows you some number of outbound emails per, but it's like 200 - 1000. High enough that most users won't ever notice, but low enough that there's no way to use the service commercially.
If an app running on my machine has subclassed the Messages app and is reading strings and sending hit strokes to the (Send) button on my behalf, how can Apple possibly rate limit this?