Quick and dirty Solidus Manual

First, find the texture you want to replace in one of the QAR files.
(Note that some textures appear in different places, so you'll have to search)
Let's assume you want to replace the MGS2 logo for the menu, like in the example on the main page.
Once you've found the file(s) you're looking for (node_title_tex.xti), check it(/them), right-click and select "Extract".


Next, open the xti file(s) you just extracted.
The program will automatically convert to TGA or DDS, depending on what image format you have selected in the "Options" tab.


Now edit the image(s) in whatever program you use to edit images, and save to either :
a) DDS, DXT5, no mipmaps, 2D texture
b) 32 bit uncompressed TGA
(You can name the file whatever you want, it doesn't need to be the same as the original)


Once you're done, go to the "Image replacer" tab and hit the "replace..." button.
It will first ask you for the NEW texture file (node_title_tex.dds in this case) and then the file to replace (node_title_tex.xti).
You should now see something that looks like this :


Last step, replacing the file in the archive.
Go back to the "File converter" tab and open the archive file again (cache.qar again).
Now select the file to replace (no need to check it this time), right-click and select "replace".
Select the newly made file (node_title_tex.xti) and voila, you're done!
(Files must have the same name for security reasons)


Note  : While extraction and XTI conversion can be done for a multitude of files at once, 
        image and file replacing are SINGLE FILE ONLY actions.
Note2 : If your software doesn't support DDS files, you can get the tools here.