If you work with lots of tempo and time signiature changes, and want to insert a section of tempo the global insert function works OK (especially with the new buttons in the tempo track) but a quick and easy way is to place the new tempo and sig at the end of the project, and then record the section you want.
use the play order track to create a play order that plays up to the point where you want to insert, and then plays the new section, then continues playing from the break point in the original material.
Flattening the play order will rearrnage the song as you wanted it, and has the advantage that you can work out the actual length of the new section and record the music before inserting it into the old material.