Ok, so: after a lot of hours of troubleshooting between the main mod and Asur Cosmetics I managed to fix pretty much everything EXCEPT for that Silverin Guard issue.
In the end I had to choose and drop Silverin Guard unit support for ALL Asur Hair Variants related mods even if they are not required or incompatible with Asur Cosmetics.
So no more Silverin Guard with custom hair from now on, sorry guys.

I have double checked in custom battle and the mod works just fine with Silverin guard.
I can only guess that you are trying to run this mod with other reskin mods that are causing said issue, please try to run this mod with only the required mods and not with other reskin mods like Asur Cosmetics and such.
This mod is meant to be used with Longer Spears for High Elves and Asur Hair Variants only.

this doesn't seem to work with the silvernguard

I'm by no means a reskinner but that's definitively doable.
I'm honestly surprised that nobody already did this though?
Are you sure that no one has released a similar mod yet?

Aight, how about Spearman armor for Archers with light armor?