Those guys had no clue and were just blowin the smoke from your woofer up your a**. Breaking a woofer in is referencing to the suspension. The spider/surroud is very strong and needs to be "stretched" for maximum lower frequency response. It does change t/s measurements as stated by dnew.
If you do want to break your woofer in next time, have the woofer out on a table (not in the box), connect it your your amp and get a cd with test tones. Play a track with 20hz straight at a volume that makes the woofer move pretty well. Try to make sure all your bass and loudness features are off or flat. You way want to allow the woofer's vent to get air into it for cooling. A roll of masking tape should be a good holder. Let it play for 20-30 minutes. Should be good to go after that.
