If I run Left 4 dead 2 via We mod, the game tells me to remove the insecure function and does not allow me to connect to the VAC servers by disabling the ability to co-op
WeMod forces the no vac flag to help protect user accounts. There is no way around this.
That is, I can’t use the trainer in multiplayer in this game?
Correct. Wemod are designed for single players, not multiplayers.