Once you've downloaded the missing stencil lot/objects, choose "Change Style" button and click on the object that has the stencil that you do not have.
Once you have the Change Style tools up on your screen, on the upper left corner you should have the presents window (saved styles):
http://imageshack.us/a/img402/2602/stencilv.png "width=640" "height=480"
Click the little folder icon (circled with red) to save a preset. Once the preset is saved, it will pop up in the preset window (the same one on the upper left), but with a different icon than the store (stole icon is by the green arrow, it's a shopping bag with a plumbob). The saved preset will have a little folder icon.
Remember to save your game after you've saved all of your new stencils because if you don't, your stencils will be gone next time you load the game.
