I do not like the idea of changing source inline like this.  If this is something that we really need, I think the proper solution, given the way things are setup now, is to fork horizon, modify the requirements, and then use our fork as the source.

That said, this will be a never-ending game of whack-a-mole. I would really rather us get to a place where we deploy an artifact. (I just so happen to have a tool for this: https://github.com/craigtracey/omnibus-openstack)  Not only would this prevent this precise failure scenario, but also let us remove a whole bunch of code, and speed up deployments considerably.