https://sims4studio.com/thread/566/shorten-mesh-blender

A few people have asked this, this my method, we will use a skirt but the same theory applies for pants and the bottom of outfits. Works with tops too, just use the nude top in S4S.

Open up S4S , create 3D mesh and clone out the female nude bottom. If you filter by female/adult/bottoms its the the first one on top left.

Click on meshes, and export LOD 0 out and save it somewhere you can find it easy.

You can get rid of the package you don't need it, its just the LOD we were after.

Open S4S again, create 3D mesh and pick out a skirt, anything above the knee, longer skirts are a different process again.

Click on meshes and export LOD 0. Go to where it saved and double click on it to open it it in blender.

Click on studio mesh 2 to highlight the skirt.

Then go to file - append

Browse to where you saved the nude LOD earlier, click on it, click on object, then click on s4studio_mesh_1.

Your nude bottom will be in the scene named as s4studio_mesh_1.001

See that little eye icon before the little arrow, click on it to hide it so you can just see your original mesh.

Makes sure you are still on s4studio_mesh_2 , press the 1 key on your number pad on your keyboard (not the top row number) and it will put you in front view.

Click on edit mode and the back face selection box in the pic below.

Press B to bring up the bounding box and select all the mesh you want to remove, including the legs, its easier as the are not where the skirt will be chopped off anyway.