This has been implemented in Commit 54958ddb6 - effective as of SuperLemmix 2.4.
To apply these per-style, place the modified levelinfo_icons.png graphic into a new folder called "levelinfo" in the style's root folder (alongside the terrain, objects, etc. folders).
To apply these per-pack, simply include the modified levelinfo_icons.png in the level pack's root folder.
PM me on Discord if you have any issues or need any help with this.