I don’t think I’m the ultimate authority here - guess everybody will use Cantabile their own way. But personally, I tend to mix just like you do: I have a number of generic patches like “Soul Organ” or “Blues Organ” that I use in a number of songs (my “Soul Organ” patch sounds great when layered with a piano and controlled via expression pedal).
And of course, I only change these very carefully, since a change will affect all songs that incorporate them. Whenever I have the urge to edit one of them, I usually rather create a copy, give it a new name and keep the old version for all other existing songs. So there are a number of “Soul Organ New” or “Blues Organ 2016” floating around that will probably never get fully cleaned up.
OTOH, there are a number of patches (aka rack states) that I build specifically for a given song. These usually carry the song name, e.g. “ComfNumb Solo Strings”, “JumpingJackFlash Lead”. I only use these for one song, which keeps edits local and unproblematic. When re-using them in other songs, I am pretty dogmatic about only using copies and re-naming them accordingly.
I tend to build song-specific patches for “signature” sounds that define the sound of a song, but my bread-and-butter pianos, e-pianos, hammonds, strings or brass are pretty generic. I just customize effect sends at song level (add reverb, delay to taste).
I do all my splitting and layering at song level; my racks all deliver simple one-zone-sounds across the whole keyboard. So, for “Comfortably Numb”, I do a lot of song state switching between a broad pad & piano patch and a split with the high strings in the upper half of the keyboard. Plus, there is a nice solo synth split (moog on right, pad on left hand) for the first solo (our guitarist refuses to play that one…).
I find it easier to manage all my racks as simple tone generators and keep all the song-specific complexity of layering and splitting at song level.
Hope this helps!
Cheers,
Torsten