Sometimes, as a manager in a technical organization, you realize you need to change technologies. In my experience, this is a change that takes place over time. So when I've used this strategy, I have hired people with expertise in the new technology and who could coach my current staff with their learning. And, I have hired people who could do the current work and learn the new technology. I paid more attention to problem-solving skills, adaptability, and cultural fit rather than technical skills. And I paid attention to the levels of the staff I was hiring, to make sure I didn't bring in people at all one level.
Let me caution you against a technique I've seen used: relegate current staff to the “old stuff” and bring in new people to use the “new stuff.” I don't recommend it. If you have some staff who don't want to transition to the new technology–ok. But my experience with technical teams is that most people want to learn and use the new stuff. If you use this technique, the team will lose trust in your ability to watch out for their interests. Since you aren't looking to help them learn, they will find a manager who will–generally at another organization.