So, me and my friend are trying to do a speedrun of the game (she is the host). But, even with server.cfg, autoexec.cfg and userconfig.cfg modified to change md_survival_mode to 0, when Unforeseen Consequences starts, the survival mode starts to count down, and we only can disable it by doing a vote. Any help?

toggle_survival_mode for host.

You can make a bind/config for each map to start off without survivalmode. Or have it toggle every time with toggle_survival_mode as a host, as mentioned. It's also pretty important to set mp_respawndelay to 0, which also can be done in the cfg file of the map. I think that's the best way of doing it.