Oh yes, there are certainly Merlin Regency AUs. I'm pretty sure there's a Merlin AU for just about anything you could mention (or else you could get one in a couple days by mentioning it in the right place).
...You realize I now urgently need to know what the right place is, because I have some I would like to mention. (Where is the AU based on the 1980s song "Opportunities" by the Pet Shop Boys? I mean, "I've got the brains, you've got the looks, let's make lots of money" - try to tell me that is not Merlin and Arthur in their caper AU, and I will just laugh at you.)
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...You realize I now urgently need to know what the right place is, because I have some I would like to mention. (Where is the AU based on the 1980s song "Opportunities" by the Pet Shop Boys? I mean, "I've got the brains, you've got the looks, let's make lots of money" - try to tell me that is not Merlin and Arthur in their caper AU, and I will just laugh at you.)