No dice, for multiple reasons. I thought that screws were holding the existing seal in place. In fact, after consulting with Lisa (she has the GM shop manuals for the van), I find that the seal is held in place by one-way plastic screw-like things embedded in the seal (I can see them in the replacement), numerous single-use plastic fasteners, and sealant adhesive. To remove the old seal, I need a special tool as well. So now I need to buy the tool, solvent to remove the old adhesive, new adhesive, and some of the plastic fasteners. The good news is that Lisa says none of these things is tremendously expensive.
It also is too cold to be doing this sort of work, as we're going through a snap of below-freezing weather here in the Bay Area. I know, those of you who live in cold climates scoff at us thin-blooded Bay Areans, and personally, I'm not too put out at the cold, other than I'm not used to dealing with wearing gloves. But I don't want to apply sealant in weather that's too cold for it to stick.
Looks like I'll have to put off the replacement until after I get back from Oregon. I'll try to remember to bring the shop manual back with me as well, or at least copy the pages that go into detail about the factory-approved way to remove and install the weather-stripping.