I have released version 2.1.1 of the script with the following changes:
## [2.1.1] = 2017-09-21
- Script can now be used offline, provided you've run through the script once online successfully (Checks if JNUSTool has already downloaded the needed files)
- PNG Check has been added, so that it will warn you if your PNG isn't valid
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I promise I didn't forget about this, just really really low priority. With the new version 2.1.1, the files JNUSTool downloads are retained after usage and not redownloaded over and over, so if you replace the bootLogoTex.tga in the (TOOLS\JNUSTool\Rhythm Heaven Fever [VAKE01]\meta) directory it will be used for your inject. I don't recall the specifications off the top of my head, so make sure that your TGA is the right dimensions with the correct depth or your inject may not even boot.
This should at least work until this is officially implemented.