As the video shows, you can use the Channels Manager to first transpose the song to C scale. And move channels to the proper channel/part for the style. Then go to multieditor (piano roll) and place a Intro Marker at the beginning of the measure where you want the Intro to start and an End Marker where you want the Intro to end. If that's all you want to create, then you can convert the MIDI to a style at that point and save the style with just an Intro. You can copy the Intro to the Ending in the Sections Manager also. Then Export the Intro to your computer HD.
Now... Load the style you want to modify. In Sections Manager; delete the Intro you don't want and Import the Intro you just created to replace it.
You can download the demo and try this for yourself. You can't save any work but you can practice using the program to see if you wish to buy it.
Joe H