I'm planning to make a barbarian using either Urban Barbarian template (for Controlled rage) or half-orc. Now my question.
When he is at 1 HP, can he ask or inflict himself 2 points of damage, so his level of damage will turn to nonlethal and he then drinks a healing potion to get ridd of nonlethal and heal a bit of more?
Your specific example is not a good one, but yes. Let's say you get knocked to negative hp and have a bunch of non lethal damage. When you get magical healing it will essentially heal twice as much, as you know. It's a nice little benefit, but I don't think there is a way to milk it to take advantage of the system.
How is he doing it?
Guarded life will turn barbarian level amount of damage to nonlethal damage whenever he is reduced below 0 HP while raging.
Half orcs are allowed to have one action when they are below 0 HP.If having 1 or more points of nonlethal damage won't disable orc ferocity, he can then use action for heal himself, which might even double the effect from cure.