to my best knowledge, the codeblock length cannot be controlled directly in our simulator. According to the CQI value and the number of scheduled resources, a certain amount of data bits is generated. These data bits are then passed to the channel coder for encoding and interleaving. Coded bits are mapped to symbols and modulated.
This process is done according to the LTE-A standard such that all the scheduled resources are utilized with a modulation and coding according to the CQI value. I am actually not completely sure, how the codeblock length is chosen exactly within this process. However, to directly control the CB, you would have to modify the channel coding within the simulator.