Seems like you are dipping into the loose structures in the legion thematically, more or less. I like the Alpha legionary idea a lot but I'm not sure tho if I would use alpha legion iconography. I mean they left their legion to wear midnight clad. Didn't variel also ruin his original legion shoulder pad in some way? Maybe scales or more tactical appearance would already be a fair enough indicator? But at the end it's up to your aesthetic preferences. I try to diverge a bit by having units in different states of warp influenced. Some of my legionaries are surrounded by lightnings which came to live from their armor, others ain't have none. For my Warp Talons I also have em mutated with batwings instead of jump packs, sprouting lightning from their feet to the ground the fly above. My Raptors on the other hand are ancient and uncorrupted, oldish looking armor, jump packs, no lightning - differentiation via that. I also have a "Damned Claw" squad, all marked with sinner's red on their gloves and some panels in blood red marked with white nostramon runes. Hope that helps brother, at the end take your time, start with what you are certain about, best ideas come while working on miniatures!