Mesh won't update

Hi.
You most likely saved the file in a version of blender that has no plugin. What blender do you have, what version of s4s, and what does blender path in s4s settings look like?

That said, you should not be importing your blend in any of these packages because it is not structured the same. ( this is not the cause of the mesh not importing)
To understand how it should be structured, open 2 part.package, export the blend again, and open it. You will see 5 meshgroups: 2 meshgroups in the calf area ( for them to disappear when a sim wears tall boots, otherwise they might clip), 2 meshgroups in the upper arm area ( for sleeves to hide armbands, otherwise they will clip) and the rest of the body. Toggle the eye icon next to each to see what is wha
To import your modified item into the same package, you would need to split yours the same way and assign corresponding cut number.

However, you dont always have to do either.
Does your item have sleeves that could clip into armbands? Yes, so it should be split the same way to hide armbands. But.... i do not know a single accessory that uses that regiontype and can actually be hidden by these sleeves. So if you want to do things right, you can split them. However, this is one of these examples where it is not necessary.

May your item conflict with tall boots? Yeah, so it should be split in the calf area.
However, generally maxis tall boots dont conflict with nude legs, only pants and skirts. So, again, you can but you do not have to do this.