Can I get a clean stamp for a B visa if I have a one-day overstay and what are my border options in Chiang Mai?

The user currently holds a tourist visa extension but faces a one-day overstay issue, making a change to a B visa challenging. They inquire about the availability of the Mae Sai border for a quick turnaround to get a clean stamp for their B visa, as well as the possibility of applying online for a tourist visa while still on a tourist visa. Commenters confirm that all land borders to Myanmar, including Mae Sai, are closed to foreigners, and suggest exploring Huay Xai in Laos as an alternative border option.