Does cold bluing steel prevent rust?
It provides limited corrosion protection. I would suggest just putting oil on it; more corrosion protection and it will not obscure the surface pattern which is  most all that separates Damascus steel from ordinary steels. As I remember regular "bluing" is a complex of ferocyanides ; Oxides of iron are red and black , brown rusts are hydrated oxides. I have now looked at Wiki and see some of the problem.  Molten cyanide salts are use to carbonitride steels;I believe these leave a blue surface- you can't do that. Another source of blue ( and straw and purple) color is different thicknesses of very thin oxide layers. I have a chart showing one hour at 540 F (in air) , or 10 minutes at 590 F, or 20 hours at 485 F will produce a blue. Higher temperature and longer time give thicker oxide. The color of the oxide is determined by the thickness. Assuming the blade is hard like Rockwell C 60, these temperatures will cause some softening. The other methods sound like they will etch the steel . Same conclusion, oil it.