CactiGuide.com

I have an interesting looking Cereus Peruvianus Monstrose that was purchased as a three-foot-high plant. The very top of the plant looks like it may have grown out of damage to the bottom mother plant. The top section is pristine. The bottom plant is covered with scars. The area where the two plants join is suspicious for having been possibly cut in the past. Should I sever the top section and attempt to grow that as a separate plant?

It's perfectly healthy, there's no need to cut it - unless you want two of them.

Absolutely agreed. If you grow it in the open air or in greenhouse the lower part of trunk earlier or later will turn into real wood and there's no need to care about it's beauty. I see it's a bit dried though it's still summer. This type of cacti needs abundant amount of feed and water during warm season. The pot is pretty spacious enough.

I think cutting it is a sensible option, if you want a nice, unmarked top cutting and a rooted, but marked base which will produce new shoots, which could be used for further propagation.
It's generally recommended to take cuttings in the spring.