Depends on your entry method. With a long term visa it should be no problem. Off a tourist or visa exempt entry almost impossible without the help of an agent.
Anonymous participant 205 No idea where you got that from. In Phuket if you stay in a hotel or hospital (even in Phuket) you need to re-file a TM30 for your actual residence.
You must report being 90 days in Thailand. The fact that you’re allowed up to 7 days after to do so is irrelevant. If you don’t report you may be subject to a fine when you next interact with immigration.
If your embassy does not provide the income affidavit (many no longer will) your only option to switch to a “retirement” visa is using banked 800k.
For the initial visa and 1st year extension that’s the only option. For the 2nd and subsequent year extensions you can switch to the 65k international bank transfers method.