Yup. Those are in the info____.pac files under /info2/. info.pac is for standard multiplayer, info_corps.pac is for Classic, and the rest are self-explanatory. You don't have to change all of them if you don't want to. The _mg files are essentially copies, as far as I'm aware you don't need to change those. The images are in MiscData[40] for all files. For the "GAME!" and "TIME!" images, you need to change the format to CMPR if you want them in their original colours - leaving them as IA4 will change them to black and white. You also need to replace InfCntGsetBase, InfCntGsetSpark00, InfCntGsetSparkBase01, InfTimeup03, and InfTimeup04 with 1x1 transparent pixels, so the image doesn't get rendered with green outlines in the shape of the default "GAME!" image.
Make sure your info.pac doesn't go over 391 KB, or the game will freeze at the "Now Loading" screen on boot. The quickest way around this is to change the file's compression type to Extended LZ77 in BrawlBox, which will buy you an extra 60 KB of space to play with (this works with most other compressed files - the only one I know of that breaks as Extended LZ77 is STGRESULT.pac).