W4rCh1ld

Yeah it because im trying to make the default emulator retroarch as much as possible, but also have the more regularly updated / more powerful / more settings exe version for some platforms too, (many examples; dolphin core / dolphin standalone, Swanstation Core / Duckstation, Flycast Core / Redream, etc etc) and with retroarch being able to get into its setting with F1, where as the non default often i want to make game specific changes before launch so its alot more often / common to want to boot the non default vs the actual default... but you have made me think that yeah i could just go with some sort of work around (which honestly is kinda dumb and far from "neat" and pleasing etc) like you've suggested, but as its not "really" for certain / specific single game instances but just because i want to access the emulator as and when i want without manually going to its folder and booting it... so what ive done is;  
Added the emulator as "a game" called it - !1 [Emulator Name], 
Set its exe as the Launching/ Application Path, 
Unchecked the "use an emulator to play this game" box
Favorite'd it. 
This launches the emulator directly, has it listed first and foremost in the systems game list (due to being called !1 and fav),
Kinda dumb imo, but it works.

So i did it and got it working, the dll simply looks at the application path, see its ends with .m3u and adds the default Launchbox multi disk icon (which i renamed m3u multidisc, as im using the neon blue disc from the neon arcade set already instead) to the list... Pictures show the settings used, which unfortunately resulted in 2 yellow warnings (shown in picture2) during the compile (NU1904) which i neither know what they are or how to fix them to make the green "perfect" compile @jayjay says to get on his Custom Badges page as ive never used this application before or "really" know what im doing at all (if he would like to explain or fix my error that would be appreciated too). The 3rd picture shows a set up games, list of badges so that the "launching" specified file ends in .m3u so adds "my" lauchbox default light blue double disk at the bottom, has its discs in the additional apps so that lauchbox has added the neon arcade blue disk 2nd down as standard for multidisc games, and each of the disks were individual stories so the same game but disc 1 and 2 are not sequential, and named to differentiate between the discs, so also showing "multiple versions" - the purple square stack 3rd down. Thanks @JoeViking245 that was an interesting solution. Ive Included the .dll too.
 
@Kefka2b you may be interested in the file? You just need a Badge image called; m3u multidisc added into the images/badges folder and the dll below in the plugins folder and turn on the plugin badges in the settings and all the .m3u files will have a badge. 
 



Badge m3u multidisc.dll