@Mark ***
There is no risk of denial. The only requirement for retirement extension is that you have 800,000 in your personal bank account for 2 full months at the time of the application for extension. There is no requirement that the money was an international transfer for the extension.
Also, if you have Kasikorn, there's a 99% chance that it will show as an international transfer anyways. And even if it didn't, you just go to the Thai bank the money was routed through and get their credit advice showing that it was international. There's no case where you are denied based only on this.