Answer: You could do that as a way of renewing them, but it is a drastic method especially since this is a relatively slow growing shrub. If you opt to cut them back hard like that, do it in late winter -- not now. Keep in mind too that while they should regrow with a regular shape, the hard pruning also has some risk of killing them.
A less drastic method would be to remove any dead wood (you should do that now regardless), then prune as needed to restore a symmetrical look. Try not to take off more than 25 percent of the branches at a time. You might need two years to bring them back into shape. These can also be sheared, so they take pruning quite well.
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