Yes, you definitely want to power it down. How many wires are connected to it? Are they mostly 22G / 4 conductor alarm wire? Any pictures of the install?
One way you could do it is to use punch down blocks. If all the wires route out of the panel in a common direction (bundled), you could number each wire and cut it, then punch it down to a 66 block. If you leave enough slack on the panel leads, you can then punch those panel leads down to another 66 block. You could then run a single 100ft. 25 pair cable between the blocks instead of individual lines. It will make it much easier to pull and route the cable and to re-attach the two blocks.