I'm not sure if this has been ever attempted. You'd have to find someone able to construct a pin converter.
Is that the only differences just pin conversion needed? The only reason I see to do this is Magician Lord since its cheaper on AES
I don't think it's possible. The main difference from an MVS to an AES cartridge is the NEO-ZMC graphic demultiplexer chip. This chip is present on AES cartridges but not in MVS cartridges. This chip is present inside the MVS system but not in the AES. So I don't think it's possible. There would be conflict with the mainboard chip and the cartridge one.
http://wiki.neogeodev.org/index.php?title=Pinouts#AES_Cartridge It looks like AES carts are 50 pins wide with MVS 60 pins wide. It says on one page: A NEO-ZMC2 or PRO-CT0 chip is used to pre-serialize sprite graphics to be output to the cartridge edge. For the PRO-CT0 carts, a NEO-ZMC chip can also be bankswitch the M1 ROM. If it's multiplexing some lines and you can multiplex them to make a MVS cart work, I'd assume you can demultiplex them for a MVS to make an AES cart work. But more commonly what people do is just move the ROM chips from an AES board to MVS board or vice versa.
It wasn't all that long ago it was an ultra common game you could pick up for $10 or so on MVS. Keep looking and you'll probably find a cheapish copy... although it's not really THAT expensive when you consider what an adapter would cost if it existed (it's not possible, though).
Arcade operators used to do this because home carts were cheaper back in the day, oh how the tables have turned...
The reason being that home users bought the carts to play. Arcade operators bought the carts to have people pump money into them and make a profit. Just like video rental, if you want to do it legit, you had to pay the price due to the fact you're making money from it many times over. And that's precisely why the arcade boards were designed not to take the home carts! Considering the price and difficulty of doing the reverse of a home conversion if it can be done (needing a sac cart, time, knowledge etc.) vs. the cost of getting an AES just to play the one game vs. the relatively low cost of a copy of the game on MVS, just get an MVS copy!!
You know, not every MVS cartridge follows that logic. Magician Lord, Nightmare in the Dark, NAN are a few games that are cheaper on the AES side.
You would need something like a viletim scart to jamma adapter and a neo geo padhack. Should be simple enough a project for the usual suspects but a little silly. You´d still get Mag lord MVS cart cheaper than padhack and scart to jamma adapter.
