No, I dont think Hologram can selectively enable and disable networks on their back end. The best way to do this is on your device itself. This is modem dependent so you will have to look at the documentation for the actual modem / cell module you are using to see how to manually select your network.
If you are using a Hologram Nova you may have to use the U-Box AT commands as I dont think their SDK has a way to do this (I may be wrong though).