By the way I forgot, is the overall stats of this HUD changed to default? does this change the, say, rate of fire as well?

the weapon Tiers are changed through "bucket" value
with 0 being primary, 1 secondary, 2 third slot, and so on

I guess it is depends on the weapon. HUD sometimes are created for the weapon that matched a modded/created weapons. As for the script, you can edit that with a VTF/Notepad++.

I dunno, I haven't been here a while. Let alone doing mods for this game. HUD/Custom HUD still suffers from inconsistency during online play. I never use this again, because of the issue I mention earlier.

So it's safe to say, it depends to whatever your liking. That covers it for me. Perhaps you should asked someone that has been sticking around longer. Like Alex D. (He change his name), because he is the expert and I just followed his leads and I haven't sticking around in here.

May I ask, is there a way to convert a HUD icon from one slot to another? like, say, a HUD for autoshotgun converted to combat shotgun slot, or maybe from smg to silenced smg, or even from one tier to another

I think that would be very helpful for some of us who've got our favorite HUDs either gone or scripted only, also those who prefer to keep things vanilla (in this case, the weapon stats)