@Zero_20
Kuriimu cannot open and edit
every file of
every game. They support the most common image and archive files and
some text files, but that's it. A list of supported files can be found in the
Kuriimu Wiki.
However, if you want to edit a file that is not supported by Kuriimu you need to write a tool for it yourself. The basic steps are a) determining if the file is compressed and decompress it if yes, b) viewing the file in a hex editor (I recommend
HxD) and trying to figure out the format (some formats are documented in the
3DBrew Wiki), c) writing a tool to extract the image/text/files, and finally d) figuring out how to put a modified image/text/file into the original game file.
That being said, it's not easy to figure out a file format, you do need some experience in programming and general concepts of storing data like images/text as binary data in a file. If you want to get started, I recommend to take a look at common file formats and how they approach this by starting with a file header specifiying the length of the file etc. like
PNG (general format for images),
CLYT (frequently used layout format for the 3ds) and
BINJ (text format only used in some dragon quest monsters games on the 3ds).
