.TEX file editing, is it possible?

[AnyOldName3]

In 'the real world' a .tex file will contain TeX or LaTeX typesetting code (a sequence of commands and text defining a document), which is why you're getting results for text editors. Obviously, this game's textures aren't held in this format, but its developers chose .TEX as a file extension for their texture files. You may well find that if you open one with a text editor, you'll see a header for a common image format, such as bitmap, png or tga (in which case you'll just need to change the file extension so it's recognised by a standard image editor), but it may also be the case that a completely wacky proprietary format was used, in which case, you'd have to reverse engineer the file format and create plugins for your image editor software so it can load and save. If you know what you're doing, this may be possible, but it's likely an awful lot of work, much of which will be tedious and require a lot of prior knowledge.