DonEduardo,
Welcome to the forums.
Band in a Box doesn't allow generations or freezing of individual bars.
If you have BIAB for Windows, the easiest way to accomplish what you are after is to use Realband. It's included with BIAB (Win). Realband does allow generation of individual bars.
If you don't have BIAB (Win), the only possibility that I can think of is to use a DAW and to export your present tracks to that DAW.
Then, save the BIAB file with a new name, unfreeze all the tracks, add your intro and regenerate. Once this is down, export your new tracks to the DAW so that all the old and they new BIAB tracks are there.
Now, working with the audio, use copy and paste to copy the intro and merge it with the existing tracks that don't have an intro.
Once the intro is completed, it would then be possible to save the files as WAV/wma/mp3 and add them back to BIAB as Performance Tracks. I suggest you have a read about these in Help.
Personally.... what I've done in similar situations as yours is...
1. Save the song with a new name. This keeps the present song and all the frozen tracks in place so that I can get back to them if needed.
2. Unfreeze the tracks.
3. Add the intro bars.
4. Generate the song.
5. Keep on regenerating the song until I get a sound that I like. When I get one track working fine, I freeze it. Now I generate again and again until I get all the tracks working as I like.
I've found with BIAB that great song generations are always available.
Regards,
Noel
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