The sentence as a whole is confusingly constructed; it is too convoluted. I have tried to sort out your intended meaning: What may be the most important thing in Brubaker conceptualisation is that it permits the possibility of different outcomes for the interrelations between various social agents at a certain moment and/or locality. This generates greater or lesser crystallisation and reification of ethnic groups, which influences the opening or closure (permeability or impermeability) of boundaries between the different groups.
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