re: are you sure that raise/lower/lift the barrier has the meaning tighten/loosen/remove the requirements?
Well no: a barrier is usually not a set of requirements that have to be met in order to access something. A barrier is normally something that stops people from accessing a place.
Unlike a bar, which is always intentionally placed somewhere, a barrier does not have to be: it can arise or exist in nature, by accident or otherwise.
To raise a barrier can mean to erect/create a barrier or to make an existing barrier higher.
Regarding the boom gates/boom barriers in your images, the boom (the red and white pole) can be lifted or raised, or lowered. In that context, certainly you could call the the boom "the barrier" and raise or lower it.