General method behind converting recursive inorder, preorder and postorder traversals of a binary tree to a non-recursive one?
Can they be reformuated and/or created from the recursive implementations in some unified way, so that I can write them out by just looking at the recursive implementations?


Yes, they can be reformulated in a unified way.

We take the &lt;pre/in/post&gt;_order recursive calls together with the visit procedure call, reverse them and push the corresponding nodes on the stack s, marking each node with its purpose: TRAVERSE or VISIT. I think the examples below explain the idea better.

Preorder traversal

So, iterativePreorder can be reformulated as

iterativePreorder(node)
  s ← empty stack
  s.push(&lt;node, TRAVERSE&gt;)

  while (not s.isEmpty())
    &lt;node, mark&gt; ← s.pop()
    if node = null
      continue
    if mark = TRAVERSE
      s.push(&lt;node.right, TRAVERSE&gt;)
      s.push(&lt;node.left, TRAVERSE&gt;)
      s.push(&lt;node, VISIT&gt;)
    else
      visit(node)


It's easy to see the above pseudocode can be transformed into the iterativePreorder procedure provided in the question by 


eliminating two consecutive push/ pop operations on the same node;
not pushing null-nodes on the stack.


In-order traversal

Skipping the boilerplate code, we get:

iterativeInorder(node)
...
    if mark = TRAVERSE
      s.push(&lt;node.right, TRAVERSE&gt;)
      s.push(&lt;node, VISIT&gt;)
      s.push(&lt;node.left, TRAVERSE&gt;)
...


Postorder traversal

iterativePostorder(node)
...
    if mark = TRAVERSE
      s.push(&lt;node, VISIT&gt;)
      s.push(&lt;node.right, TRAVERSE&gt;)
      s.push(&lt;node.left, TRAVERSE&gt;)
...


The iterativeInorder and iterativePostorder procedures cited in the question don't look like the above code because they make use of the traversal patterns arising in those cases. Like the fact that under in-order traversal we go straight to the leftmost leaf of the input tree, visit it, go one level up and do the same thing for the right subtree of the current node, etc.