Is it now possible to convert a Non-O visa to a Non-B visa in Thailand?

What type of non-O visa are you on, because if you never got an extension, and entered last January, it has already expired, because the type O you get from a Thai embassy is only good for 90 days, and must be extended inside the country. If you have been on amnesty this whole time you are going to have problems, as the amnesty is not an extension of your visa. It is only an amnesty from overstay fines. If it was by chance a multi-entry, it still had to be extended every 90 days by leaving the country. You could leave the country and return, thus renewing it, but as far as still being in Thailand after 90 days, it has expired. There are only a very few immigration offices that have given a type B to persons on amnesty, and it has been for qualified English teachers, with their university degree paperwork, and not every office does it. Contact immigration to find out.

Have you already had at least one extension of stay? If yes, then all you do is cancel the current extension (they will give you two weeks from cancelation if you request) and then apply for an extension based on work. Always been possible. You are not changing the visa. You are changing reason for extension of stay, which is allowed. If you have not had an extension yet nowadays they make you get the first extension for the same reason you got the visa and after that you can change the reason. Talk to your local immigration office to see what documents they require.