You probably will need both ExtendSim 10 and 2024 during the transition period while you convert your files from 10 to 2024. The transition period should not exceed six (6) months. Deployment of the software after that period shall not exceed the licensed quantity of concurrent users of ExtendSim.
As long as each product has its own License Manager installed on different Servers, it is not a problem to install two or more ExtendSim Floating license products on the same Client device and/or use those products on the same network. The license file on a Client device product will point to the correct Server's License Manager assigned to manage that product.
It's a little more challenging, but certainly doable, to have the same License Manager on one Server manage both your ExtendSim 10 Floating license and its upgrade, ExtendSim 2024. For details on setting this up, see Using one ExtendSim License Manager to manage two Floating licenses.