This. try to use also a clean rom as a base.
Thanks for your software.
Based on experience and testing. There's quite a couple of things that needs to be improved.
The software itself:
1. The software assumes that you'll be using the base NDS VC extract of the title-id "WUP-N-DADE", compressed with WinRAR (this is also another issue, might be) with the filename rom.zip.
Testing:
This isn't going to work if your "base" NDS VC extract is not "WUP-N-DADE". The software renames .nds files specifically to "WUP-N-DADE.srl". i.e. if I'm using a base NDS VC of, let's say, "WUP-N-ABCD", when loadiine loads the NDS emulator, assumingly, the emulator extracts the rom.zip file and specifically searchs for WUP-N-ABCD.srl, in which in reality, it is not that resulting to black screens. (for readers, search and research what I mean about the title-id)
The Fix:
It may be against the copyright and/or piracy but have an option to choose "which" base NDS VC to base the file name from, users would have to figure out what their base NDS VC is. OR better yet, have an input space to type the X letters title-id (this should be the way to go). Users MUST still know what the correct filename to use and/or title id of the base NDS VC.
2. The rom.zip file it produces, isn't a zip archive, but instead a rar archive with the filename of .zip.
Testing:
I've found out that the software compresses the file with the "rar" archive instead of being a "zip" archive, this can easily be missed because of the file extension used as .zip.
The Fix:
Although the software utilizes WinRar to compress the file, make sure that it uses the "zip" archive method.
Although I'll be honest, I have not fully tested number 2 as as soon as I have found out the issues of me experiencing Black Screen one my WiiU, I found the two issues above.
Screen resolution:
Also, with regards to changing the screen resolution, have at least as an option, but I tried changing them to a 16:9 ratio (1280 720 on TV, cannot change to 1920 1080, and 854 480 on gamepad), it does not look good. It is not a "real" widescreen view, it is a stretched 4:3. I don't like it, but some people might do. I would recommend to only change the 10th screen mode on the .json file.
Meta folder and file creation:
If you are looking to let the software itself create the icons and backgrounds needed, I would recommended to extract the icons from
http://nintendo.wikia.com/wiki/Category:Nintendo_DS_box_art_(North_America). Note that these are US Cover arts, and it may not have all of them. Resize to 128x128 iconTex.tga file. With the background, it's a bit difficult to pin point one location to get it from, but probably have atleast an option there for users to either drag or drop the image file they want or open it to resize to 1280x720 bootTvTex.tga (for the tv background) and 854x480 bootDrcTex.tga (for the gamepad). With this as well, depending if implemented, users may have different background from the tv and gamepad.
Output Location:
Have atleast an option to choose where to output files, instead of just being in the desktop. or preferably, the root directory of where the software is.
These are all my findings with the software. Thanks for it.
Also, if helpful, my setup is as follows:
WiiU is in my sig.
Windows 10 Pro x64
WinRar x64 (don't know what version, too lazy to find out but not lazy to type these words

)
Edit:
If you want to edit/modify the NDS emulator,
visually, more: have a look on the assets and/or images folder inside of the NDS VC, you should be able to find there the .png background of the original NDS (first version), amongst others.
Possible changes:
1. Change these to other images i.e. NDS Lite, NDS XL, etc.
2. Change screen size on the .json correspondingly to above, if necessary. (you can even change positions if you want)