system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40k] Can Eldar still become Dark Eldar?
gpt
Absolutely, yes. The various qualities of the Dark Eldar pertain to the over-exposure to stimulus and the gradual soul-draining power of Slaanesh. ALL Eldar are subject to the latter, and the majority protect themselves with Waystones, which act both as barriers and proximity siphons, containing the spiritual energy rather than letting it bleed into the Warp. 

Any Eldar without such protection will gradually have their soul bleed energy. The more they engage in certain actions which align more closely with Slaanesh, the stronger this effect will be. If the drain becomes stronger than the souls natural growth, they will eventually die. 

Dark Eldar are past this threshold, and require huge amounts of stimulus to encourage soul 'growth' to keep going. The most efficient way to do this is pain, which they eventually absorb like a sponge from their surroundings. 

ANY Eldar subjected to the criteria above will become Dark Eldar. It still happens, and is in fact a rather common fate for those who spend too long on the Path of the Outcast.