from the way you describe how you worked originally are you sure you used BIAB for your original tracks? i first got BIAB on floppies and with it got PowerTracks (PT) free so i created a rough song in BIAB, exported to a midi file then did the editing of midi in PowerTracks - changing notes, time values etc.

these days you get RealBand (RB) free with BIAB which will open midi files on separate tracks, allow you to edit midi easily. it's the descendant of PowerTracks and is much easier to use working with midi.

you already have RB so why not open your old midi files in RB and see if you can do what you want.

the phenomenal power of BIAB comes at a cost - you have to work in a BIAB way. RB is so much easier although it still has some of the power of BIAB.