Crape myrtles react favorably to pruning, even heavy pruning. Just make sure to prune in late winter or early spring so you don't miss out on this year's floral show (they bloom on new wood). Topping the tree (removing the central leader) is not generally recommended unless you're going to keep the tree smaller, say, under 20 feet. That would be the strategy for making the tree grow wider.
Luke Miller, editor
Garden Ideas & Outdoor Living magazine