You can get paid from work done before you moved. But once you move any additional work would need a permit.
Proper way would be to setup a Thai company and get a work permit via that. Not sure what your original country of origin is but if US check out the treaty of amity, it gets rid of a lot of the downsides of having a Thai company as a non-thai.
And yes patching your product would count as work. Good things there are no bugs or issues with your product.
DTV wouldn't let you work in Thailand either. It lets you work remote for a company outside of the country not in country.
Several people have had the same issue of not planning far enough ahead and actually having their visa before their travel date. What you are talking about is what they have been doing waiting in country until they get approval then border bounce to switch visas.
The risk is in the embassy wants you to come in for some reason you are SOL.
But since you are already in a different country it isn’t that much extra risk.