Iv done them many times. The first time I think I was about 19y/o. You need to have a tool to compress the spring(these are available at your local parts store for rent usually. Some of them actually have little clamps that hold around the spring so its impossible for the spring to let go (but take a little longer to set-up). Another option is to take the struts out yourself (entire assembly), and take it to a shop for them to just compress and take the old strut out and put the new spring in).. Not sure if many people here replace the springs on the S90's but I've heard cars over 10 years have a high chance of the spring breaking I guess it might depend on the car but for example a civic with 10y/o springs, your asking for trouble if you don't replace it... I know Volvo's are much higher quality though..
--
1998 Volvo S90 SE (Black Cherry) 220,000+km