SDLPoP cannot create .DAT files.
To create modified .DAT files, you need to use the program PR.
How to do that is described in the document that Norbert linked to here:
After you download PR, also read the documentation (in the doc/ folder) carefully, in addition to the document that Norbert linked to.Norbert wrote: ↑March 12th, 2018, 9:46 pm Either modify the data/ files of SDLPoP or MININIM, or read this document.
If you don't understand any of it, I can't help you.
Note that PR uses .bmp images instead of .png images. So, to use your modified images with PR, convert them to the .bmp format.
PR has its own forum board, by the way.
Good luck!