You remember how long it took for native SE Asian Android phones to emerge? Not long. It may be best to wait until local Chromebooks are tested in the market… It probably won't be too long, the price point, battery life, and functionality seem to be appealing for a variety of educational and professional uses.
Failing that, the best option will be to buy a USA Chromebook, and then use wifi hotspot/tethering to provide it with network access.
As you surmise, the CDMA data used in the Chromebooks is USA-only (more or less), and limited to the carrier Verizon. It's unlikely that, even if the hardware was upgradeable, that drivers would already exist that could control the modem/carrier combo you have.
Simply put, if you can't wait, try to leverage your cellphone's mobile data.