What options do I have for my Non-Immigrant O-A visa before it expires?

The new visa stickers may say 'Valid Until'

May I ask where the "enter before date" is on the visa? I checked my visa and didn't see any on mine.

This has come up before and discussed. At that time my friend and another similar case went like this. Her O-A first year expires Oct 1, 2018. She went to Singapore in late April (only a few weeks ago)... she came back and was stamped in with one year. So her second year will expire in April 2019. She then went to Krabi Immigration and bought a Reentry Permit. She will leave Thailand on June 6 and will not return to Thailand until after the 'enter before date' (first year expiry). Krabi Immigration discussed this with her and said her second year until April 2019 would be preserved.

Seems to me while the OP has little time to do this... A one day flight - to KL and return in about 8 hours - At the KL airport - enter Malaysian Immigration - then go back through - stamp out of Malaysia. Then the return flight lands at Bkk and he is stamped in until May 5, 2019.

I have done the 8 hour turn around at KL Airport myself for other reasons.

Alternately - take a one day land border run on May 5.

I had same situation and got a one year multi entry stamp at Hua Hin for thb 3800 very simple and valid for one year then 45 days before that expires you need to do a proper renewal bank state medical etc

your options are

get a single re-entry permit before you fly out which when you return will stamp you in until March 2019.

OR

dont' get a re-entry permit and when you're out of the country apply for another year-long, multi-entry Non-Immigrant Type O-A visa

Until I saw Tod’s answer, I would have said you can buy a reentry permit for 1000 baht, either at Promenada, or at the airport. And that should preserve your visa. But I’m sure Tod has a good reason for saying otherwise.

You will be out of the country when the visa itself expires (so you will not get the second full year free by exiting/re-entering just prior to the enter before date on the visa).

AND

your current admitted until stamp has too much time on it to apply for an in country yearly extension, because you can only do that when you have 30 days or less left on the stamp and you have until march 2019 :O

Remember you would need a re-entry permit when you fly out in May in order to get stamped back in for the expiration of this current stamp March 2019 because the multiple entry part of your visa expires on August 9th.

You have limited options :/