Have not tried updating the SD socket symblo yet (still keeping both) or changing 0805 pads to squares from round. I think for that I have to delete them on the schematic, add them in again, and then see if they will fit in the same space on the board.
Assuming the parts have the same number of connections in the same order then you can just use the 'Replace part' tool which seems to work pretty well when people have the wrong package for a chip or similar.