Can I select the Keysight 34401A's front/rear terminals using a software command?

No. The 34401A terminals can only be changed using the mechanical switch on the front panel.If your application requires automated, multi-channel measurements, you should consider the Keysight 34970A Data Acquisition/Switch Unit. This instrument offers up to 60 channels of Keysight 34401A-quality measurements in the same half-rack size. Data Acquisition Switch Unit