http://gamevixenzone.undertow.club/tools-utilities-19/resident-evil-5-arc-tool-29/
The above is a link to the tool you need. What you going to need to do, if you want to change the model effected.
Is first step is to extract ARC uPl01ShebaNormal which should be one of the Sheva to Jill model mods on this post. Then your going to extract uPl01ShebaCos1 from the NativePC folder. (A vanilla version that has not been mod from the game files.)
Now your going to look at all the "model" files in both folders and very careful rename all the file from uPl01ShebaNormal so that they match the names in uPl01ShebaCos1. Now some of the files in uPl01ShebaNormal need to be move to the right folder in uPl01ShebaCos1 for example Pl0d.jex is hosted in it's own sub directory in Sheva Tribal aka uPl01ShebaCos1 under pl0d instead of pl12. pl12 is where most of the files for the tribal model can be found under uPl01ShebaCos1.
Most of the files your going to copy from uPl01ShebaNormal can be found under
uPl01ShebaNormal >> Pawn >> pl >> pl01 >> model
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Which after you rename them to match the names in uPl01ShebaCos1, you'll the write over the model files in uPl01ShebaCos1....
uPl01ShebaCos1 >> Pawn >> pl >> pl12 >> model
It's a tedious process, but if you match all the files perfectly and then Repack the Arc. The Jill model under BSAA uPl01ShebaNormal, will now work perfectly for Tribal uPl01ShebaCos1.
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Or you could just copy over your current uPl01ShebaNormal file with another uPl01ShebaNormal file mod, which is what I recommend.