I am the UK reseller of repairs to the Saab 9-3 4 button fob, I replace the covers, fit new switches and swap the key holder over.

Swapping the key holder. Due to the difficulty I have used rather large pictures You will need to carve away a lot of the rubber covering the fob as you cannot remove the key holder without damaging the cover. You will also need to remove the plastic over the key holder as well.   Here the rubber & plastic is removed, and one clip is visible, see how horrible old covers get when they need replacing.   The metal clip can be disengaged by using a modelling knife blade, the two other clips, use small screwdrivers, or small nails.     Cleanthe keyholder with meths or white spirit, then a gentle scrub with washing up liquid.