Weapon change.

Let's not delve into the structure of mods; we'll immediately move on to the mechanics of attaching a model.

Open the map editor; it will look something like this. I've indicated with an arrow the important window; don't close it; this is the "map properties tree."
image 1. I'll be inserting links because the screenshots are large.

Let's set up a unit; let it be the leader. It doesn't have LOD models (all units up to the Horde Lords have separate models for the map with a smaller number of polygons; by the way, in the GEM mod, all these models were removed).
I've selected the leader; as you can see, the map properties window has changed; now it shows the object's properties.
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If you click on the text in the Shared line, a button with an ellipsis will appear; click on it.
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The object window opens; just as we went into Shared, you can go further, for example, into the model, from the model into the skeleton, and in the skeleton, copy the UID to extract it from data.pak, but we'll talk about that later.
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Okay, let's go.
You need to go into the animset; there are a lot of animations; go into the idle stance.
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Here we are in the animation; there is a line called Effect; it's empty; you need to create an effect; click on the line and, instead of the ellipsis, click New.
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A window appears. If we simply write Idle.(Effect), this file will appear in the folder with the leader's animations; this can create confusion, so it's better to write, for example, T5bEffect/Idle.(Effect); then, instead of a file, a folder with a file will appear, and all subsequent files will appear in the folder; click OK.
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We need to go into the effect; this is a list like the animset; in it, we create an item.
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In this item, as we created the effect, we also create a file to attach the model; let's call it Weapon.
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We go into it; we need to specify the bone to which we attach the model, but this field is not visible; we need to make it accessible; to do this, click the right mouse button in the free space and click Show Hidden.
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The field has appeared; this is the last line; you need to enter the bone there; for the leader, the weapon is R_Sword.
I entered the archer in the model line for the test; the result is that we attached the model to the axe.
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If you don't know how to view the bones in the skeleton, write, and I'll explain; I just don't want to do anything unnecessary. I've already been sitting here for almost an hour writing.

If you didn't understand how I selected the archer, write, too.