We study how unsolvable planning tasks can be modified in order to get solvable. We apply Katsuno and Mendelzon's distinction between update and revision and show that (1) the modification of the initial state is an update, (2) the modification of the goal description is a revision, and (3) modifications of the set of actions can be reduced to initial state modification. The input of all three belief change operations being counterfactual statements (instead of boolean formulas), existing belief change operations do not apply as they stand. We show that both the counterfactual statement and the two belief change operations can be captured in Dynamic Logic of Propositional Assignments DL-PA, where we use a variant of Forbus's update and Dalal's revision operation to model belief change.