Of course TTN supports MAC commands. Not all of them (yet), but surely the most important ones. And there’s a lot to be found online:
- The LoRaWAN 1.0.3 specification.
- The code is open source.
- TTN supports ADR, which also uses MAC commands.
- There are several questions about it on this forum.
- There’s even the quite specific Can I send MAC commands to the node?
For an example on how to decode the MAC commands in the FOpts field, see TTN Node - link check does not work?