For the IncomingRunner, it should be easy. Create a subclass of IncomingRunner, and override the _get_pipeline() method. Then override the QRUNNERS variable in your mm_cfg.py to use your new subclass rather than IncomingRunner. Again, untested, but a bit easier to do, and much safer on the brain the above two half-baked ideas.

Well, if I wanted to hack the code, lots of things would be easy... but I was thinking of "some codified thing that lets an admin do customization things" rather than "unsupported code hacks". I was probing whether or not others thought there was a need; primarily you.

If we're talking about custom pipeline modules, we're talking about Python coders, so that's not a horrible thing, but: since modules are already so separate, it would be useful, perhaps, to have some sort of "insert this into the pipeline" mechanism that is also separate and robust wrt changes like GLOBAL_PIPELINE changes.

I suppose subclassing isn't so bad, but it's a bit heavier mechanism than I was thinking...but that may just be a function of me thinking like a procedural programmer. :)