Ability to initialise field values for a transition screen

Similar to POST functions that are set AFTER a transition is executed (after pressing e.g. the 'Resolve issue' BUTTON), it would be very useful to also be able to set PRE functions (values set in the transition view after the Available Workflow Action LINK is pressed = BEFORE the button is pressed).
Thus, it is possible to set default values in the transition screen, but the user can still change it.

E.g.:

• press Available Workflow Action link 'Resolve issue'
  (invisibly, the assignee is set to the Reporter by the PRE function)
• enter the screen which is set in the Transition View of the 'Resolve issue' transaction
• here, the assignee is set to the default value Reporter; but the user can still change it
• press the Resolve issue button to confirm