While holding a rail blueprint, press G to swap all rails between the ground and elevated layers. That's pretty much it.

(The hotkey is the same as whatever you use to switch rail layers while using the rail planner.)

Demonstrations

Limitations

The mod does its best to determine where rail supports are needed in order to build the new elevated rails. This isn't a trivial problem to solve, so very complex blueprints might lag or fail to find a valid solution. This can be refined in the future, but currently the mod handles a wide variety of situations quite well.

Scripts are not able to modify the contents of blueprints in the cross-save blueprint library. However, the mod will work if you are holding a blueprint from the "game blueprints" library, or a blueprint stored in your inventory, or a copy/cut selection. Overwriting the contents of a blueprint in the "game blueprints" library requires an opt-in via per-player settings.