I'm not completely positive I can fully follow what your workflow is, and what specifically your question is, but this is how it generally works: Each soundpool has a default tempo in which it has been produced. However, it's possible to use loops at a different tempo and combine loops from soundpools with different tempo via the magic of time stretching. When you first import a soundpool loop into an empty project, the project main tempo will conform to the tempo of that soundpool. If you then go ahead and import further loops with different tempos, those loops will conform to the project tempo, i.e. unless you specifically turned off that option in the program settings, in which case you will just get a big mess with loops being out of time with one another.
You can also change the entire project tempo after the fact via the main BPM setting next to the transport controls and time display. This will result in *all* contained audio loops being adjusted to the new tempo via time stretching.
Further to what Ralf said, you should read the part in the manual about Song Maker. It uses random loops from the selected Soundpool. It can be helpful as a basis for making your own adjustments and additions, that is all. Once on the track, you make adjustments manually, including changing out loops. In order to do that, you have to learn how. See the tutorials and read the manual.
If you want to change the Soundpool, then you have to delete everything and make your selections from a different Soundpool. However, I suggest that you simply delete the previous version and create a new one using the Soundpool that you want.
Your latest post is very confusing, sorry. Does it have anything to do with your original question (about Soundpool tempi) or is this a different problem? If so, please start a new thread with full details of exactly what you are wanting to do.