Alternating number of lines for the shell between layers Is is possible to have alternating numbers of lines for the outer wall between each layer? So, say, one layer will have 3 lines for the wall, the next layer, 2, then the next layer 3, then 2 again, and so on? Even better, if I could group them in twos: two layers with 3 lines, two layers with 2 lines, repeat until done.

I use Cura, but if other slicers can do this I'd like to hear about it, too.
It is possible to get an alternate extra wall in Ultimaker Cura, the option is called Alternate extra wall. It can be used to catch the infill more firmly, strengthening the print.

From Ultimaker support:


  Alternate extra wall
  
  This setting adds an extra wall every other layer. This way the infill gets caught between the walls, resulting in stronger prints. For example, if you set the wall line count to two walls and enable alternate extra wall, it will print two walls on even numbered layers and three walls on odd numbered layers.
  


I've used this option frequently, but I'm not aware of any option that you can change the amount of layers alternating. You can do that probably with the option to set different options for different sections of the model, see e.g. "Different infill in the same part".