You cannot change projects seamlessly.

You can however, change between patterns and parts seamlessly. When you switch to a different pattern bank (e.g. pattern A01 to B01) all the tracks can have new samples assigned to them. Same with when switching parts.

Download the free sound packs for the Octatrack (http://www.elektron.se/support-and-downloads) and look at how parts and parameter locks are used to make use of a large list of samples in just one project.

The only thing you cannot change seamlessly within a project is the BPM, you’d have to adjust it manually every time you want to raise or lower it. I could be wrong though, haven’t even tried that before…