Photoshop and some patience.
Ok, I had some time today and searched through my old Orbiter installations. The files that need to be changed are in the Textures\Cockpit folder. Everything seems to work as it did in Orbiter 2010, with the exception of the top screen info-view which had been completely overhauled in Orbiter 2016.
For the MapMFD you can revert to the old version by using the line MFDMapVersion = 0 in Orbiter.cfg (or Orbiter_NG.cfg, if you not using the inline client).
Just remember that compared to the new MapMFD version, the old one had limited functionality (only one zoom level, no terminator line, etc..)
I have attached a zip file here with all the changed textures from Orbiterroot\Textures\Cockpit. Remember to keep backups of the ones you are using now, in case you don't like them.
MapMFD looks for .vec files located in the Config\(Name of body)\Data directories. vec files are lists of the coordinates of the contour of the maps . I can't recall if there is a tool that can convert a vector drawing to a .vec file, as I suspect the .vec format is a custom one for Orbiter. A vector drawing in .svg file format is in a "human readable" form and the coordinates of the vector path are listed there, so it shouldn't be too difficult to convert an svg vector drawing to a contour that MapMFD can read. Never tried it myself though.