Sure. Always good to do ones research. To my knowledge, mRNA vaccines (Moderna and Pfizer) can be "mixed and matched" without hesitation. Some doctors even suggest those who had two jabs of Moderna to get a BioNTech/Pfizer booster, as the latter has a slightly lower dosage, which is equally sufficient in providing the booster effect, albeit with less side effects. I can testify to that. The booster shot came at lesser side effects than the second Moderna shot came at the time. If you had Sinopharm or Sinovac, both will be euqlly applicable as well - and be a huge improvement in protection, alike.
Not at this location. Moderna is currently only available for free at Bang Sue Station. But no walk-ins there. With pre-registration only. But Pfizer is equally good - especially if you had Moderna before, like me.
That does not mean of course they don’t run out of mRNA shots way before that. So if people are interested in an uncomplicated, well organized vaccination, I would also advise to make use of this opportunity soon.
Cannot promise anything - this is Thailand after all. But it is likely on for at least the remainder of this week. Rumors have it though, they might run out of Pfizer at some point.