It's fine, I will try fix this myself.

Ah, sorry to say but I don't think I could fix that. I'm not well-versed enough in modding especially when it comes to creating/editing scripts. At the end of the day this is just a very basic edit of someone else's mod.

Put it on the top of the mod list isn't useful at all, but I think I found the issue: the weapon scripts "weapon_upgradepack_*.txt". There is a section near bottom part where it defines "TextureData", they used "vgui/hud/iconsheet2". I think that's why your icon_upgradepack_*.vtf doesn't work.

Couldn't find anything conflicting in both local and workshop mods, guess I will prioritize it in the mod list order.

@Leon not a clue tbh, there might be some conflict with your mods that the game isn't detecting.
maybe try putting this mod on the top of your mod load order

@Fusion Mine still shows the default icons, and I didn't see any conflicts among the enabled mods, do you know what's the problem?