Can I extend my 30-day arrival stamp at Chaengwattana for another 30 days?

Yes, 30 days with exemption stamp.

yes, since August 2014.

@Bryson **************

Yes. SA citizen get 30day extension on a 30 day visa exempt stamp.

@Bryson **************

correct, countries under bilateral agreement can get 7 day extension for a visa exempt stamp. If they come with a SETV than they will get 30 day too.

Russia is actually in a different category to most other countries, they get a 30-day stamp but it is under a bilateral agreement rather than the Tourist Visa Exemption. I don't believe the Russians are affected by the two land entries rule for example. You can see here there is no mention of Russia in the countries that qualify for the 30-day exemption extension but South Africa and most Western countries are listed: -ThailandVisa.shtml

Just to point out that the rules may be different depending on nationality and what happened to a Russian may not apply to you.

Bryson, where are you getting that information that it changed? My understanding is that most nationalities who get the 30 day visa exemption CAN extend it by a further 30 days at immigration (including South Africans).