Modifying or resizing the shape of the furniture will probably be easier than modifying the notecards and scripts inside the engine.
Making a pillow or a dance pole taller in height will lower you on an animated design, making it thinner on the X-axis will raise you. And the legs of a massage table can be lengthened or shortened, or parts can be hidden under the floor.
Make a copy of the furniture before you start editing. Then right-click the item you want to modify and select “Edit”. Now it should be highlighted in blue and/or yellow.
Check the Stretch box on the edit window. You will now see white boxes around the item. Click on these with the left mouse button and drag them towards or away from the furniture, to make it smaller or bigger.
If want to resize only parts of something, check the box before “Edit linked” as well. Then click on the part you wish to edit. You will see red, blue and green boxes as well as white boxes around it. With these, you can resize in one direction only.
More information on Second Life’s building and editing tools can be found on the Second Life wiki.