Yes, but be aware to avoid cutting off flower buds and avoid pruning if frosts are imminent as this could result in the plant being weakened and suffering through winter. In May time, it’s quite normal to cut some perennials down by a third of their height (this is called the Chelsea chop and coincides with the week of the Chelsea flower show) in order to encourage a larger profusion of flower heads and prevent the plants from getting too tall and straggly.