NO, you can only work for the company mentioned in the work permit and in the areas mentioned in de description of labor.
NO, with a expired work permit you are not allowed to work and have to apply for a new year but depending on leniency of the Ministry Of Labor where this work permit is issued.
Many offices now allow people to apply during the last 45 days of their stay for a new Extension of Stay based on being over 50 years of age, the old regulation was during the last 30 days.
In you case if your current Extension runs out of Dec 27 you can apply starting 28 Nov for sure and maybe as early as 13 Nov.
Why would you not extend your marriage visa now? What if the Extension of Stay based on being unable to travel due to Covid (landborders are open) get denied?
What do you mean with a marriage visa?
Is that the Non Immigrant O visa based on being married to a Thai National OR the Extension of Stay based on being married to a Thai National?
NO, if you are on an Extension of Stay and use a re-entry permit you will get stamped in to the same date as your permitted up to xx/xx/xx already in the passport.
Alternative: Leave without a Re-entry permit and start all over again with buying a NEW Non Immigrant O-A visa before you make your way into Thailand.