correct. I have this problem too. My due date is mid March, a month I do not want to be in TH every year. But I have to restart the process to change the date. I hope for new visa procedures beginning 2025 if the EU/EFTA gets FTA agreements with TH. If.
could be now, but my 1st one laster December, after I returned, was approved. Try it. I know that the absolutely first has to be done in person. In Hua Hin, maybe different.
You have to change your visa into the new passport at the immigration. The same time you can make a re- entry stamp. Before the yearly extension of the non-o you have to change it anyway.