Most Effective way of developing a new GC for D

[Per Nordlöw]

I'm gonna play around with creating a GC that alleviates some of 
the uses described in

https://olshansky.me/gc/runtime/dlang/2017/06/14/inside-d-gc.html

What's the most effective way of incrementally developing a new 
pluggable GC for druntime with regards to prevention of 
really-hard-to-find-bugs?

I'm aware of the run-time flag added in 2.072:

https://dlang.org/changelog/2.072.0.html#gc-runtimeswitch-added

Is it inevitable to rebuild druntime everytime I make an update 
to a new GC? Is so what's the preferred way of selecting a 
modified druntime in a standard installation of dmd on a Linux 
system (Ubuntu 18.04 in my case). Will Digger makes things easier?