How to stop blender from recalculating normals? I have a mesh (a rock wall) that I would like to split into pieces and export each piece for a game engine.  The mesh has a smooth, undulating surface and when all the sections are merged into a single mesh, it looks the way I want it to.  However, when I split the mesh into pieces, Blender recalculates the normals along the edges causing a very visible change in shading.

I would like Bender to leave the normals alone, or maybe give me some way to edit the normals manually.  Can I do this?
I created a Blender add-on for this exact purpose called TiNA which allows you to easily transfer normals between objects. TiNA basically turns the somewhat overwhelming Data Transfer Modifier into a set of more comprehensible operations.
There's a special branch for those using Blender 2.80 beta.



 Hotkey           | Operation 
------------------|-------------------------------------------------------------------
 Alt+N            | Transfer Normals from selection to active object
 Shift+Alt+N      | Transfer Normals from active object to all other selected objects
 Ctrl+Shift+Alt+N | Clear Custom Normals data for entire selection
 Alt+W            | Wrap Normals


In your case you could transfer the normals from an unsplit duplicate by selecting all objects, and - with the unsplit duplicate as your active object - hitting Shift+Alt+N.