The "BASE" command is just an AutoCAD command, therefore you can use it on footprint symbols. We have as a standard that all block have their insertion point at 0,0,0 with the base also 0,0,0. If a symbol is created from Wblock, then the entities are moved so that the insertion is 0,0,0 and the BASE is also changed to 0,0,0.
There is a button to check near the lower left corner of the dialog box that may be checked to hide existing devices.
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