texture, no - but you can use entities and some logic.
tf_filter_damage
disallow damage type bullets (or allow only drown for total godmode, as long as they don't really drown)
trigger_multiple
placed in spawnroom(s) or wherever
OnStartTouch !activator SetDamageFilter FilterName
I use the same trick to make "safe rooms" on my maps where players can congregate at their leisure without having to combat.
to remove the damage filter, you can add an OnStopTouch