I did it exactly the same last time during my extension. You only need to ask for a single re-entry permit for the under consideration period and explain why. I returned back on time before the under consideration date was expired and no problem at all during arrival

It depends of your local immigration office where you do the extension. I did the first two years with an affidavit of the Dutch embassy, but my immigration in Khon Kaen didn’t ask for an apostille of the MFA

You can go on a visa exemption for 30 days and one time extend it with another 30 days. If your Thai visa is a E-visa and you will receive it after you enter Thailand. Then you can use this one after a border run

I did it in the beginning of the year after applying for my yearly extension. Got the in consideration stamp and asked for a single re-entry permit that’s valid till the end date of the consideration stamp. The IO was surprised but explained that I work abroad and that’s the reason I have always multi re-entry permit during the period of my yearly extension. Was no problem at all to get the single re-entry during the consideration stamp period, and out/in at suvharnabumi airport within the consideration period also no problem at all