On the 87 the memory box gets power from X30 under the driver foot rest just for constant power to save the settings. The motor power comes from the two auxiliary 25 A fuses under the relay cover.
On the 93 it looks like they upgraded the memory controller so that it did not need the separate backup power - there is a reference to this in the FSM that they changed the memory circuit so that it did not lose the settings when the power was disconnected. The 93 just has the two 25 A feeds from the relay box.
I would say that there should be no reason to cut any wires when doing this swap. If you find that something needs to be cut I would think twice. Remember that the connectors can be opened (with very few exceptions) and the pins can be removed and even resoldered if necessary.
I would highly recommend getting access to the online FSM and ETM and have it handy on a computer in your work space. You can register at w124-zone.com and have access to the same info as on startekinfo.com but with a better HTML interface. Also they somehow got hold of a cleaner copy of ETM than the one available directly from M-B.
I would also make use of the EPC, that will help you see how things fit together. And I would be lost working in the garage without being able to listen to Pandora or iheart radio.
. So a computer in the garage is an invaluable tool...
I am an electrical engineer, I play with control systems, so issues like this are what I live for at work. If you get stuck on something let me know.