Arms stuck to sides in CAS

I recommend using a mesh as similar to the one you want to convert to use as your clone as you can find. I also recommend that you replace similar parts of the original mesh with similar parts of the new mesh. For example, EA meshes often have a tiny square off in its own cut number. If you replace that with some giant chunk of the new mesh, you can run into issues like the one you describe because the game will be confused by this slot ray setup. If the Yoda robe is the closest thing you can find, definitely try using that. The Grim Reaper outfit has a lot of mesh groups. You may have to condense those into a smaller number of mesh groups to match the Yoda outfit's structure. When you are condensing, try to make the condensed mesh groups of the Reaper outfit as similar as the mesh groups you are trying to replace in terms of position and size. Give that a shot and, if you run into more trouble with it, post the original and your work in progress so someone can take a look.

Keep in mind that each mesh group of the clone (the Yoda outfit in this case) is associated with slot rays that tell the game where the hands should be in relation to the Sim's body. If you replace some large mesh group positioned around the hips/thighs with some tiny square of mesh located in the arm this will confuse the game because it is now thinking that little square should be treated like a big mesh chunk in a different location (and vice versa if you replace some tiny chunk with a big part of the mesh). While Studio allows manual editing of slot rays I do not recommend this as it is very complicated and no one has done any significant exploration of this option.

I've added relevant documentation about slot ray intersection data in the CAS/Pose tutorial section that may help to illustrate the above information. You can find that HERE.