Yes, there would have to be a difficulty change.

It is a bitcoin network fork that does not look for complete consensus. It uses the full blockchain history up until the point the spinoff occurs. The fork will be done cleanly so that no replay attacks are possible. The market will then be able to decide how each side of the fork/spinoff is valued. This will be similar to the ETC and ETH situation except for with a lot more planning and done a lot cleaner. Our website www.bitcoinforks.org has a lot better explanation on it.

We've been discussing what kind of hashing power we can gather just from old ASIC miners that have been turned off because they are no longer profitable.
We'd like to see how much hashing power you have if you would be willing to point it at a bitcoin spinoff. Let us know so that we can tally it up.

We don't expect to get everyone involved at this early stage and most users are lurkers anyway but it might be interesting to see.
Spread the word on twitter with the handle #MineBitcoinAgain.