Inline entity form

Drupal Commerce: Edit form for commerce_line_items to change order positions after checkout

One thing I missed within Drupal Commerce's (commerce.module) flexibility was to change line item values in already checked out orders. This is for example important, if you use custom fields in line items and want to change the values on users request (for customizable products for example).
I had to search a bit to find a robust solution, but finally I am very happy with the solution I'm describing in this blog post.