We are re-habbing a 70-year-old house that mainly has blown-insulation. We had to remove the ceiling and insulation in order to raise the pitch of the roof. We saved the insulation and wonder if it is OK to re-use it?

If it was relatively new maybe. However when you removed the insulation I am guessing you compacted it. The air spaces are what prevent the heat transfer.

I would say probably not. When you go to sell the home do you want to explain why the insulation is 30 years old.