Im no expert, so I might be wrong, but I think it could be done
You just need to modify the parts of the application binaries that load, process, and render the graphics. Then you have to repeat this process for every operating system/processor that the version of Tibia you are using supports.
While this is technically possible, it is practically impossible due to the difficulty in finding the parts of the binaries that perform those functions, and the whole thing crashes and burns if you miss even one tiny bit of code that does anything with the graphics.