Asking for a friend who has dual nationality. Can you leave Thailand on 1 passport, and then use the 2nd passport on arrival in the new country and use this to get a whole new set of SETVs? Thanks.
TLDR : Answer Summary
A dual national can leave Thailand using one passport and enter a new country with a different passport to apply for a new SETV (Single Entry Tourist Visa). However, while it may help during applications at Thai consulates, there is a possibility that immigration databases might connect the two passports. Additionally, there are no legal issues with switching between passports for visa runs, but frequent entries might raise questions from immigration if there's a long history of staying in Thailand on tourist visas.