I don't really remember, but I think when I tried unscrewing the screws they just kind of rotated in place and didn't seem to really unscrew at all, and didn't come out all the way like I had imagined they should. I found it you just pull on them they pop out, I think it was 2 pieces...
I'll go look I my trunk so I can be more helpful.
Ok, my screws unscrewed easily. But then I had to pull out the things they are screwed into so that I could pull the liner back. I don't know if you could pull the pieces out if they are still screwed together, but I remember doing that for some reason. I tried putting them in after I screwed the two pieces together and it didn't just slip back into place like it did without the screw in it (to answer your question they will go back in). If worse comes to worse, they are only plastic, if you have to break them I don't think they would cost much to replace if you had to pay for them, and they don't seem to be a super essential piece anyway(your trunk liner won't be flying around without them).

Hope that helped.