Yep, you can replace with pretty much any small 12V bulb. You might want to use 14V ones instead to prolong their life. I've also used 12V green LED's which won't ever need replacing.
Maplin sell plenty of wire ended ones that are suitable although some are a little tight in the green lens but do fit. Their 12V 80mA ones are smaller than the Saab ones but work the same.
This one is fine BT43W, this one in green PG79L
3mm green LED CJ67X , 5mm green LED CK49D
The only thing I'd say is that the Saab bulbs are about 4mm so if you want to use the 5mm bulbs, you can't use the green lens or you can if you cut out the "fins" that are moulded (you'll see when you do it).
I used a 3mm green LED without the lens and that was fine too.
It really is just a case of popping out the switch, then pull off the front and go at it with a soldering iron.