combining ea meshes

Yes, in ts4 community it is called “frankenmeshing” and you can find many tutorials about it if using this word.

If a package is referencing resources (textures, meshes, tuning, etc) from expansion packs that the person does not own, they will not be able to use it.

So if you will modify and replace the mesh but leave everything else as is, it won’t work.

Depending on the type of resources that are missing, the object may show up in their game but not the same way as in yours (something will be missing). So you need to warn people that the item requires an expansion pack.