I have a character with a long tail, and I wanted to keep the 'main body' in the center too. I've actually have a similar issue with long sprites. That way, everything would become centered in the same way and it would line up properly again. I think it might be easier if you chose a standard size for your assets and put your smaller fighters and monsters into that larger size. That will probably cause undesired behavior when it comes to passability collisions and event detecting and such.
So what you're asking isn't just shifting the image, it's also going to mess with how it works interacting with anything on the map, because it will be taking up one full tile (where the middle of your graphic, the actual ship is) and an additional half on the top and bottom. Your ship graphic takes up 2 tiles, and the ship is pointing through the middle of that (essentially the nose is on the dividing line between the tiles). More in-depth answer: In this specific case, you're asking for something screwy. I suspect you would need to commission that plugin, because I don't recall ever seeing anything like it (someone else might have a suggestion). General answer: you would need a plugin to change where the graphic is being drawn in relation to the tile it's on. Click to expand.I understand what you're talking about.
