Is it possible to legally take 20kg of prime vacuum packed Australian frozen grain-fed oyster blade beef into Thailand in my packed luggage?

Sounds like special operations.

Possible, but I've no idea about the legality. That said, I know someone who regularly brings back a suitcase packed with beef, lamb etc and has never had any problems.

I tried it once.....it did not end prettty. nobody cared. all the stress was useless

Yes, but you would need an food import license from the FDA, which costs 15,000 baht and would require you to obtain a work permit, along with completing other onerous processes.

Which is why most people take a chance and just do it.

This meat is only for personal use. I have seen Japanese air hostesses with little cool-boxes with one cut of vacuum packed beef. Might just try that.

Vacuum packs should be chilled not frozen, but I think trying to keep it chilled would be too risky.