@Fa***
what is the reason you want to do it in EUR? One thing to note, if you intend to transfer it back out, is that Bangkok Bank at least, but I think other Thai bank FCD accounts, charge 0.5% of the entire amount to transfer EUR back out. This is in addition to their regular transfer fee. On 800,000 that would be 4,000. It's not an unbelievable amount of money, but it is ten times larger than their wire transfer fee which is 400B. There may also be a 500B charge on the way in, from the Thai side.
If you intend to spend the money in Thailand eventually, and the aim is just because you don't want to convert it all right now, you can ignore all of the above- in that case it works out basically the same cost but you can choose when you want to do the conversion.