These are not working with the API directly. It's just Discord's web client trapped in Electron, with JS/CSS injection and tracking stripped. The reason for this is that if you touch some API endpoints of Discord in an uncharacteristic for a normal client ways, your account gets banned immediately. Of course it's still detectable, but Discord does not really care. It's a measure against user bots, not against those who put in a CSS snippet to make the background pink.

That said, if you want to try living on the edge, give Discordo a shot.

Tbf those third party clients and clientmods are already against their ToS just just aren't baning anyone for using them (yet)

The last time I used Discord, I thought all of these third party apps are against terms of service and have your account liable for deletion if they want. I'm not sure how common that actually is though.

I think they used to allow them outright before, or at least were very lax.

RIP that one CLI Discord client. That had all I wanted out of Discord for 90% of the time I have the app open.