92 Supreme rear struts

I need to replace rear struts on my kids supreme. Manual says I need to compress fiberglas spring and remove it before removing struts. Is this really necessary? why cannot I just jack up side and relieve compression, and then replace strut? There is no coil over or compression on strut itself. GM manuals can be descriptive, but muddled!
Can anyone help?

I just changed the rear struts on my 94 last week. You don't have to remove the fiberglass spring. The new struts should come with a bolt to cage the auxillary springs if you have them. Use an angle finder to check the camber at the rear hub before you remove the old strut, so you can set the camber before tightening down the new strut, if you want to avoid the alignment shop. Other than that it's pretty much like a shock change.