I like to add chemicals and scents during the curing process. However, I also frequently apply scents to each individual bait during fishing. This allows me to freshen up my baits with more scent, and to try different combos.
Hunt - If you are new at curing eggs for salmon, I would start with a proven chemical cure such as pro-cure, pro-glow, fire cure, etc. That should get you to a good mix of sulfites, salt, and sugar.
To experiment with scents, simply cure as directed on the bottle. Once the eggs juice out, add scent into the juice and mix the entire contents (eggs, juice, and scent) well. The eggs will reabsorb the juice and the scent along with it. I certainly have not dialed in the magical cures, but trying different combos and scents has definitely put a lot more fish in the boat.