KiCad does not support footprint variants yet the same way Altium does. We’ve discussed it and think it would be good to add in the future, although there isn’t any work immediately scheduled for it.
BobC / BobZ - just to clarify how this works in Altium (and some other commercial tools): you can have a symbol with multiple footprints assigned to it where in KiCad you can only assign one. Then at layout time you can swap between them quickly without changing the schematic or browsing the entire library of footprints. This is commonly used to set up SMD passives with multiple pad sizes, for example you could have the normal 0402 and “large 0402 for hand-soldering” assigned to the same part, set the larger one to the default, and then switch between them during layout if you find a spot in the board where you need to use the smaller one.
Currently in KiCad you can swap the footprints around at layout time, but your options for swapping are the whole list of available footprints from the library, not a “curated” list of a few options that were previously determined to be valid swap options for the particular part.