Hi,
If your specific breadcrumb trails are already saved as separate tracks on your unit, then its easy - just delete the tracks that you don't want and keep the ones you do. You can do this either directly on your unit, or using Humminbird PC.
If you need to edit tracks - eg cut a small section that you want to keep and discard the rest - then you need to use another application. The free edition of ReefMaster will let you import tracks as GPX files (run them through HBPC first) and then edit them graphically on top of background maps - crop to range, delete, filter on depth, delete individual points, rename etc. Then you can export as GPX and run them back through HBPC to get them in the format required for the unit. I made a post about track management
here - the only thing in that post that you can't do in the free edition is consolidate multiple tracks into a single slot.
thanks,
matt