Probably just take the model for those swords and use it to replace something else.
1 - First open /data/db/itemdb.xml and /data/local/xml/item.english.txt to find the item entry.
2 - In the text file, CTRL+F for the name, finding the below line.
54083 Gan Jiang and Mo Ye (For NPC)
3 - Now we know that it's entry 54083, so go to the itemdb and search for ".54083" to find the below.
<Mabi_Item ID="44022" blah blah blah
4 - That line has all sorts of info about the item, in this case it also mentions...
File_MaleMesh="weapon_c4_npc_ftaa_sword"
So that's the filename of the weapon's model, and it's in the c4 (chapter4) category.
\data\gfx\char\chapter4\human\tool\weapon_c4_npc_ftaa_sword.pmg
5 - So now that you know where the model is, copy it.
6 - Then find where another sword's model is supposed to be, say, Fluted Short Sword...
\data\gfx\char\human\tool\weapon_pluteshortsword.pmg
So you take the ftaa_sword pmg file, rename it to that filename and put it in that folder.
Then when Mabi loads, it'll go to load the "Fluted Short Sword" model, but end up loading the FTAA one.
(Though this method assumes that dual-as-one-item weapons aren't set up strangely, never poked around with their internals.)