If have a multiple entry non-immigrant O visa based on marriage with a Thai wife, wich is still valid for 6 months.

I will be applying for a 1 year extension based on income.

Will my multiple entry non immigrant O visa be canceled as soon as I apply for the extension?

Or will it be canceled after the extension is approved?

Will I loose my visa in case the extension is not approved?

The visa will remain in your passport. But you will lose any extension of stay if you use the visa for entry rather than a re-entry permit after you make application for, or receive, an extension of stay. So unless your application is not approved it will no longer have any value to you.

Thanks for the perfectly clear answer.

The immigration officers in our local immigration office had different opinions about this.