Um. In that case I don't think I understand exactly what it is you want.
Forgive me, but I am not sure you have adequately defined what YOU want either. The tool offsets will control the Z axis which has the spindle mounted on it, but if you also have a 'knee axis', then in practice that is separate from the Z or spindle axis.
If you want to make complex decisions about whether the required vertical movement can be handled by the Z/spindle axis, or whether you will ALSO need to move the knee up/down to get within range - that is going to require a rather complex macro. This macro may end up setting a tool offset to handle the movement of the knee.
Or am I way off target again?
Cheers
Roger