So I'm looking to make some giant snakes to scare the squeamish players in my game, but I don't see anything about constrict that says its affected by size increases (from adding a template) and a lot of the constrict granting abilities don't say if they do or not. I would assume that since it does say X damage for medium X-1 for small, etc. that it doesn't scale but it might also be that it assumes medium creature damage and I'm supposed to calculate from there. Does anyone know for sure?
So the new question is does slam progress?
Not just equal to slam, but equal to the attacker's primary natural attack (whichever attack allows/activates the Constrict ability).
In the case of constrictor snakes, that's the bite attack which gives Grab and Constrict.
Which template are you adding? Does that template add damage to the snake's bite attack? If so, then the Constrict ability is increased by the same amount.
For fun, drop the Gigantean template on a medium constrictor snake and its bite goes from 1d4+4 to 3d6+20, and so does its Constrict ability.