More than one variation associated with a song part

A Question, I have a Rackspace file grouped by instruments and each rackspace with variations by themes. Is it possible to assign more than one variation to one part of the song?

Why not just create a new song part(s) and assign the other variation(s) there?

What would be the use case?
This does not really make sense.

Each theme associated with a Rackspace requires the loading of one or more add-ons, so in a GP file I must have as many rackspace (sum of instruments) as songs. What would it be like to create a Rackspace per instrument, create as many variations of the instrument as themes, and associate as many variations as instruments need a part of the theme? The load would be faster, take up less memory and have more flexibility in the allocation of the widget, since they all have the same destination.

OK I understand.
Set predictive load to for example 12.
Create a Set List with Songs which use in sum 12 rackspaces.
When you switch to that Set List all rackspaces are loaded into memory and the switch between Songs and Songparts will be smooth.

Or you disable predictive load but then all rackspaces are loaded into memory.

Thanks PianoPaul, this is how I have my structured file, but it occurred to me that different variations (instruments) could be stacked in a part of a song and that it would be easier to build a repertoire with different instruments by part , it was just an idea