...use small ally pop rivets for the refit. It's a bit fiddly on the re-fit but ultimately it works a treat
I've just done this and I would recommend it as the best, neatest method. If you're tempted to use some screws a little larger than original beware- where the trim goes down the front pillar anything longer than around 9mm will see the end of the screw touching the inside of the pillar and begin to distort the metal, pushing a tiny point shaped indentation into it from the inside. It very nearly happened to me yesterday! Luckily I was watching for it happening as I screwed in a stainless self tapping screw; with a light shining directly onto the pillar I noticed the pillar begin to move a tiny amount and I still had a couple of turns left on the screw so I withdrew it and luckily there was no damage done. Could've been a costly error though...
Also, another thing to remember when refitting these trims is to apply a tiny bead of sealant along the edge of the body before pushing the trim on. They had a none-setting seal, similar to a 'dumdum' type of stuff, right along the full length of it from the factory when new. This is, I assume, to provide a waterproof seal along the gutter where it joins the body, otherwise water would manage to get under it and it would become a perfect rust-trap.
Andrew.