When you're in the Chord Sheet of Band-in-a-Box®, hitting F5 on your computer keyboard within any bar of your song will bring up Bar Settings (specifically, the "Settings for Current Bar" window).

This window allows you to adjust the number of beats per bar, tempo changes, patch, style, and harmony changes for your song!

Learn more in Chapter 6: Making Songs | Settings for Current Bar of our Band-in-a-Box® 2018 for Windows Online User Guide.

An excerpt, to get you started:

Settings Apply to Chorus #
You can specify the changes you make to happen for every chorus and/or a specific chorus. This applies to bar settings like tempo changes, style changes, RealDrums changes, patch changes, volume changes, and harmony changes.

Number of Beats this Bar
The initial time signature of the song is determined by the style (e.g., Jazz =4/4, Waltz =3/4). In some songs you will want to change the time signature, for example, you might want a single bar of 2/4, or 8 bars of 3/4 time. This option allows a change of time signature during a song.
The change takes place at the beginning of the bar and continues until a new time signature change is specified. You can select from 1 to 4 beats per bar. Time signature changes are printed on the Notation/Lead Sheet.

Example: A song in 4/4 time with a single bar of 6/4 time
The maximum # beats per bar is =4, so we will split the 6/4 bar into 2 bars, a 4/4 bar and a 2/4 bar. Insert a # beats per bar =2 at the beginning of the 2/4 bar, then restore the time signature to 4/4 by assigning # beats per bar =4 for the next bar.

Tempo Change
If you want to change the tempo at a certain bar of the song, then use this dialog to type in the new tempo in beats per minute. The tempo change takes effect at the beginning of the bar and remains until a new tempo change at another bar is inserted. Alternatively, you can specify a percentage change in tempo.

Key Signature Change
You can have multiple keys in the same song with the new key signature shown on notation. Select the new key signature you want from the combo list and you will see the new key signature drawn on the notation at that bar.

...and more - this Window is a GREAT way to customize your song!