How do I prevent CiviSMS from converting my URLs to longer clickthrough-aware URLs?
You can install this extension: https://github.com/PalanteJon/coop.palantetech.nosmsurltracking.  This will automatically turn off click-through tracking on all mass SMS messages.  There's no checkbox (unless someone codes one in), so it turns tracking off on ALL messages - but if you need tracking on a single message, you can disable the extension temporarily.