Generally speaking, yes, and it would still work.
Problem is, while the main camera is a module of itself, the selfie camera is in the top module that houses other functionality, too. So if you would dismount.the top module, not only the selfie camera would be missing, but e.g. the earpiece speaker and the headphone jack, too. You may work around those misses with Bluetooth, but being Bluetooth, this can be a hassle.
There would be visibly something missing where the cameras were before … but don’t rely on common sense when dealing with people unknown to you before 
.
You can 3D-print your own case. You can design it to your taste and needs.
Remember you would have to deal with the selfie camera, too.
See the iFixit Teardown for pictures, or have a look at this video …
While the process is fairly easy, it involves disassembling/ reassembling screws, and with users reporting contact problems of unknown origin over time inside the phone with the modules in general, the modules are clearly not designed to be disassembled and reassembled several times a week.
The modularity is primarily meant to aid repairability, it’s not meant for casual pop-off/ pop-on.