The only change is that on placement, Railroad, and Big Power Poles (Plus bob-mods version of them) will, on placement, become neutral and indestructable and so, while still functional, will not be attacked by Biters or spitters, ever. This does not apply to rail stations, trains, train cars, signals, or any other power poles however.
This is mainly intended to use with Rampant AI, where establishing outposts is essentially impossible since you have to defend every single power line and block of track between it and the main base. This mod lets you provide power and train routes, but doesn't allow conveyer belts.
Use the "Deprotector" item if you want to make the objects vulnerable again, or make them invulnerable again. Do this before taking the mod off, or if you need to blueprint stuff. (Blueprints don't work on neutral stuff)