AfterYou said:
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(Basically, the problem I have is that when I re-compress my edited files using crystaltile2, the compressed files have a larger file size than the ones originally on the ROM. And Crystaltile2 will only let you replace files in a NARC with files of same or smaller size, meaning some compressed files can't be edited if they don't get re-compressed enough).
Even if the files are smaller than the original, you don't want to reinsert them because this will cause errors. It will cause the game to crash when it tries to load the image. What you want to do is decompile the original narc into individual files, replace the old files with your modified files, and then recompile a new .narc file. Once you have your new narc file you can rebuild the ROM.