, did you read the post? It says “Travellers who are unable to complete the TDAC before arrival and do not have internet access at the point of entry will be assisted at designated help points located at immigration checkpoints. This assistance is intended for exceptional circumstances only.”
Yes, you can. Tell to the officer at passport control you need a re-entry permit. You will be given a direction to re-entry permit counter (small room behind officers). Official fees are same. 1000 baht for single, 3800 baht for multiple. You need filled form and photo.
Or you pay extra 200 baht fee then you bring only your passport. They do forms and photos for you.
And 1-year extension is not "single entry", it is with "no entry". You may not want to forget to apply for a single- or multiple re-entry permit when you get a whole 1-year extension.
you cannot get marriage visa without proof of legally married to a Thai woman. If you visit Thailand to marry her, you cannot get non-O before your marriage.