title: Woocmmerce how to allow only one product in cart of certain type
body: <p>Sounds bizarre for me to ask this, in woocommerce is there anyway to have a specific product, which could be controlled via the product id, to only have one in the cart, so in our scenario they select one or the other, if they try to re-add to cart it simply replaces or swaps that item in the cart.
  Our main products would not then be affected by this rule.</p>