title: update a constraint with Pulp
body: <p>Suppose to have a linear program and a constraint of the form:</p>
  
  <pre><code>4 x_1 + 3 x_2 ≤ 10
  </code></pre>
  
  <p>and that you want to update it to </p>
  
  <pre><code>4 x_1 + 3 x_2 + 10 x_3 ≤ 10
  </code></pre>
  
  <p>or to</p>
  
  <pre><code>3 x_2 ≤ 10
  </code></pre>
  
  <p>In order to do that, I "rewrite" the constraint from scratch, like</p>
  
  <pre><code>prob.constraints[0] = ...
  </code></pre>
  
  <p>but for a very long constraint this is very inefficient.</p>
  
  <p>Is there a simpler way to add or remove variables from the constraints?</p>