The capacity of a compartment can vary during the course of a simulation. To do this, you must set the Constant property to false (or the ConstantCapacity property in SimBiology versions before R2019b). Then, you can change the compartment capacity using things like repeated assignment rules, rate rules, and events.
You cannot add additional components of any time (compartments, species, parameters, reactions, etc.) during the course of a simulation. So you cannot directly simulate an increasing number of cells if you need to treat each of them as distinct entitites in your model.
However, you may still be able to model cell growth in SimBiology. The feasibility and exact approach will depend on your goals, but let me offer an example:
Create a SimBiology model of a single growing cell and add a parameter to the model that counts the number of times the cell has divided. Add an event to implement cell division. This event divides each compartment volume and the amount of each species by 2, and increments the counter for the number of cell divisions. Then, simulate your model for the desired time and analyze the results.