When using C&B 12.12 in MC 1.10.2, using structure blocks to import a structure from another saved world, bits from Immersive Engineering blocks will usually appear as Flat Colored Blocks bits. Similarly, sometimes bits from Flat Colored Blocks will simply not appear at all when importing a structure that contains them from another saved world.

C&B doesn't support cross world structure blocks, this is because of the compressed format that it uses. And it requires some verity of forge patch to enable support for this.

In the mean time you might try Recurrent Complex, it should have support for C&B.

How bad does it get if you always use registry IDs in TileEntityBlockChiseled.writeNBT? I don't see Forge adding a special method like te.exportNBT().

Its a petty sizable inflation for the cross world format for some blocks, in the range of over 300% in some cases, just because simple blocks compress very well right now, but if I were to use string id's in all cases it would case significant inflation in size.

I'm currently of the mind set that its not worth it for this.