As mentioned, it depends on the immigration office. I use Nonthaburi immigration which basically follows Bangkok immigration rules and they specifically told me no need to file a new TM 30 unless you leave and re-enter the country.
Email them. They are extremely quick at replying to queries online. Generally speaking rental income does count towards the $80k a year passive income requirement for the wealthy pensioner LTR.
Border bounce but be careful. It seems as though you already did at least one border bounce this year. You’re allowed 2 a calendar year (via land border).
UK embassy in Thailand doesn’t provide an affadavit of income so that route won’t work for you. Ask your local immigration office what the requirements are for a 90 day Non O retirement visa. It’s almost certain that you will need 800k baht in a Thai bank account before applying for the visa.