Can I apply for an extension of stay at Savannakhet after obtaining a Non-O Visa (Marriage)?

Jimmy, Robert has spelled it out precisely what you have to do to get a One Year Extension of Stay.

But please note the Non Imm O Visa you get in Sanannakhet is for 12 months - However it only comes in 90 day increments (permission to stay)... At each 89-90 day mark you have to Exit Thailand and Reenter - do a Border Bounce. Upon Reentry you will be stamped back into Thailand for another 90 days. This is a routine event - nothing to it except the time, travel and expense of going to a neighbor country's border. And also take note - you can perform this out and back in - from 15 minutes to 30 minutes to 60 minutes - then you are back in Thailand. You do not go to the Thai Consulate in that neighbor country.

NO, You have to apply for an Extension of Stay at your local Immigration Office. Proof of funds 400.000 Thb 2 months on your Thai bank account or income statement from Embassy with minimum 40.000 Thb income a month, copy ID page, visa page, entry page and tm6 of passport, copy id and house book wife, if rental house, copy id and house book landlord, map to house, copy marriage certificate, Kor ror 2 from Amphur, copy first and last page of Thai bank book on your name, passport picture and one picture you and wife in front of house with house number and 1 inside the house. 2 set of copies needed. You can apply 30 days before last day of admitted to stay stamp in passport.