Generally speaking you don't change your tax residence. You either are or are not a tax resident of one or both countries, but as I understand it if your income is generated in France you continue to be taxed in France whether you are a tax resident or not
I don't pay tax via PAYE, I have to file a tax return and have had to do so for many years, now I am no longer tax resident I still have to file and pay just like before.
no idea what PIT is. But its not about tax withheld at source. I haven't been a UK tax resident for 8 years but I'm still required to complete a UK tax return every year and pay any tax due as a result.
nothing to do with withholding tax. All income arising in France is subject to French tax. Just as all income arising in the UK is subject to UK tax. There can be some adjustments due to Dual Tax Agreements where tax on certain types of income is paid in one country or another but I'm not aware of any that affect earned income.
that's complete nonsense. Anyone who spends 180 days or more inside Thailand in a calendar year automatically becomes a Thai tax resident in that year. Having a bank account is not relevant. Having a visa is not relevant.