Hi everyone...just a head's up if you have dual nationalities....I tried to leave Thailand on my south African passport and reenter from Penang overland with my British and they would not allow it...even though I had a 2 month visa in my other passport...so the only way to switch passports is if you fly in again!
TLDR : Answer Summary
A user shares their experience of trying to leave Thailand on their South African passport and reenter using their British passport. Despite having a visa in the British passport, they were not allowed to switch passports while crossing the border overland from Penang, indicating that passport switching is only permitted if one flies into Thailand.