Do the part configurations permit using something like 10/32 bolts, large backup washers (or similar), and elastic insert locking nuts? You might even use plastic bolts.
Make sure that the "easily replaceable" part is more likely to break than the other part.
I did this on a 97 Mustang with under bumper "air deflectors" that originally were secured with LARGE OD "pop rivets" that needed an expensive tool to install.
You might even consider "ty-wraps" depending on the part configurations. Black is best for UV resistance. The tywraps will be stronger than the plastic parts they are securing but depending on the configurations may allow some "hinge" movement when you hit a cone.