Well, the minute you cut the stem that initiates multiple shoots at the nodes so you will likely lose that singular "palm tree" shape. You can get 5 or 10 side shoots emerging simultaneously. If you want to prolong the singular form you have to replant the topped portion and toss the base. That gets dicey because the lower portion of the topped stem sometimes tends to rot. That's why I suggested to float the topped portions for a couple of weeks before replanting or just continue to replant them as their lower stem goes soft until they harden and stay put. In a few weeks though you'll have the same dilemma. Stelleta can get messy and is a dichotomy, no doubt. The only reason I endure the tribulations is because it produces some of the most spectacular photo shots I have ever taken. If you're not fussed about keeping that singular shape then just toss the tops and manage the side shoots as they emerge. The more CO2 you have the less likely the stem will rot, but the more side shoots you'll generate.