Okay, it's relatively easy to get access to those extra decorations. In modern LabVIEW's they start at 986 (0x3DA) and then, when you increment the index, you go through the columns from top to bottom, looking at@flarn2006's picture in the very first post of this thread. To find the memory address of the image index, you may use any debugger or helper tool of your choice, like CheatEngine or ArtMoney etc. In Heap Peek you can get the address of the decoration object and the image index assigned to it. Then in CheatEngine/ArtMoney search for that index and pick up the nearest higher address. Now you may alter the value at that address and watch how the decor is changing on the panel.
In fact,@flarn2006discovered not extra images, but extra handler procedures, that perform the drawing with the Drawing Manager API. It looks like LabVIEW has many of them reserved for some purpose. Or maybe they're just leftovers of the early versions. Indeed, some of them could be useful in real applications. But I still don't see how a modified decoration could survive the save without hooking into LabVIEW internals at least.
Seems, like it works! Here's the VI with the most decorations from the first post: Extra Decor.vi
And if anyone wants to recreate the VI, here's the script that I used: Adding Objects (Extra Decor).vi Not guaranteed to behave well on anything different than LV 2022. Also requires a couple of SubVIs from here.