I'm confused by your last response, sorry. If this doesn't make sense below, my apologies.
Let's say you have permissions set up somewhere, or a filter based on assignee, and these are looking at the xpath:
/my:myFields/my:containerGroup/my:repeatingGroup/my:assignee
which is a repeating node and has three rows, Bob, Sue and Vito
then most likely permissions are granted to all of the three because those are the values in
/my:myFields/my:containerGroup/my:repeatingGroup[1]/my:assignee = Bob
/my:myFields/my:containerGroup/my:repeatingGroup[2]/my:assignee = Sue
/my:myFields/my:containerGroup/my:repeatingGroup[3]/my:assignee = Vito
You could create a separate field, outside of the repeater, and call it my:CurrentAssignee. This would be a single (non repeating) node that stores only the current assignee, and you could assign permissions or filter based on that xpath.