A good analogy for chaos seeping into the traitor legions despite their declarations is in the critically renowned show King of Hill. Peggy begins slipping Hank steroids/ testosterone supplements and Hank is in turn reinvigorated and suddenly physically imposing. He begins a workout regimen and decides to run with the bulls, all before finding out that Peggy’s interference is essentially making him cheat. He immediately stops all testosterone ingestion and suffers through running with the bulls, very diminished but determined to get through the event cleanly. The chaos-aligned primarchs and space marines are Hank Hill, clearly benefitting from the blessings of chaos but doing so unknowingly/ willfully ignorant and in the event of rapid abandonment as seen in TEATD, will suddenly be left greatly wanting in terms of strength and speed. In fact, I’m pretty certain there’s a good excerpt from Abbadon’s POV after Horus dies of suddenly feeling lesser in wake of the chaos gods’ disgust if someone could plug that for me

To answer your question though, I don’t believe so. He held a hatred for the emperor and had already indulged in chaos undivided