I have an A600 with a Kick Start 3.X and it loads Workbench.Library during boot from the hard drive.
This makes upgrading fairly easy.
If I had put a Kick Start 3.1 in my A600, which has Workbench.Library in r.o.m, is OS 3.1 modular enough to point to a new Workbench.Library during boot?
I think the answer is Yes.
It looks like this can be done with most of the O.S. components.