You can change the Block Configuration code for GPS satellites by going to GPS Signal Sources File --> Signal Control--> General. This can be seen as H1 in Figure 1.
H2 displays the drop down menu with all the block configurations available. if you wish to apply a Block configuration to all satellites you can do this by pressing the 'all' tab highlighted in H3. Alternatively you can apply different configurations to each individual Satellite by selecting the satellite number as displayed by H4.
Please note that the Block Configuration only applies changes to the navigation data and does not effect the simulated satellite signals.