Seems like I need to clarify the "l4d_csm_infected_access" cvar. This does apply to the infected team at all, as this plugin cannot be used on the infected team. For those who want to change their character on the infected team, I recommend using
Zombie Character Select
If you want access infected models as a survivor, set l4d_csm_infected_access to 2. If you want both characters and models, set l4d_csm_infected_access to 3.