I did mine with it up. so simple and very little risk of getting hurt.
I was trying to get the tension perfect and messed it up the first time. I called a garage door man and he said he could do it to perfection. $50 later he left and never came back. I learned enough from him to do it myself with the door closed. Actually didn't even have to use the vise grips because of very little tension on the springs.
just thought I would pass that on, might save someone some money.