I don't see why this can't be distributed as two RTEncoder files, one for the new geometry and another for the new CR2.

With the obj file it would only need to contain the chest geometry, this could then be loaded from the new cr2 using 'objFileGeom' like so:

actor abdomen:1
 {
 storageOffset 0 0 0
 geomHandlerGeom 13 abdomen 
 }
actor chest:1
 {
 storageOffset 0 0.3487 0
 objFileGeom 0 0 :Runtime:Geometries:SuperBoobs:NewChest.obj 
 }
actor neck:1
 {
 storageOffset 0 0 0
 geomHandlerGeom 13 neck 
 }

Or even better the cr2 could use geometry swapping as used for the Dawk's hip, so that users have the option to swap between the new chest and the standard one.

P.S. I say "chest" geometry, but in V4 wouldn't  the breasts be in the collars? Don't know, don't have V4. But the principle is still the same.