Load Leveling Shock Replacement?

My 03 has "Load leveling" rear shocks. Is that the same thing as self leveling? I'm planning to replace with Bilsteins once I confirm what I need. They sell an extra spring for the rear shock to replace self leveling. Can someone tell me if that is easy to install or if there are known issues installing after market shocks? I did a search on this site but didn't find this info.
Thank you.

Mike

I have searched archives on this site and others. How can this question have not come up? Surely people are replacing these type of shocks with others???

dude the shocks are shocks, never installed aftermarket ones on load leveling, but as you might know, those are air shocks. make sure you replace them with air shocks and the air fitting will clip on.. and no idea what you mean by the spring