VS1 to VS2 upgrade

Hi,

I am having a VS1 (dual engine) to VS2 (dual engine)upgrade.  Based on the procedure it mentioned that I should have 32 + 8 (40 cables and ports) available to cater for the FE/BE/WAN.   The local comm will need extra 4 more cable to ISL VS1 and VS2 local fabric.

My question here is the based on the procedure it seem like the upgrade will be done one at a time.   I will have VS2 mounted on the same rack as per VS1.   I am planning to re-use back the same cable since I am going to do 1 director at a time.

I was wondering is it really a must that we should have those 40 new cables laid and assign for the VS2.  The only thing I can see is that this will avoid any cabling error and ease of rollback.