Can I convert a Volunteer non-immigrant O visa to a non-immigrant B employment visa without leaving Thailand?

It is generally not possible to convert a Volunteer non-immigrant O visa to a non-immigrant B employment visa while remaining in Thailand, as visa type changes are usually required to be processed outside the country. The ability to change a non-immigrant O to a non-immigrant B may also depend on the nature of the employer (whether it's a BOI company) and the passport held by the individual, with some countries restricted from changing their visa status without leaving.