Altium - Use an existing component symbol for another component
You need to create an Altium PCB library that contains all of your SMD footprints. Once you have your PCB library created, open the SCH library containing the symbols you want to reuse, select the part whose symbol you want, and open its properties (double-click it in the SCH Lib tab, or right-click it and choose "properties"). Then in the "Models" section at the bottom right of the properties window that pops up, use the "Add" button to add your footprints.