I'm pretty sure GMs had this tested before, it was not so long ago after Fairy Auction, but i didn't really hear any news since then...
God i have too many characters. Just call me Bisu and let's end this -_-
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Transferring a character between accounts IS possible and costs 2 GM Services. If I remember correctly, the emails of the two accounts must be similar. Also, transferring would be a lot easier if the empty slot is the same number as where the character was in the previous account.
As Ptah said, this was offered after a Fairy Auction not too long ago to test it out, but I'm not sure if anyone actually tried it.