The PGA and its resistors are pre-built and get configured at your needs by setting the properties in the module. There are no elementary analog building blocks like transistors resistors etc.
You can always use OpAmps in Creator with external resistors if you need
something specific the PGA cannot provide, like IA configuration, specific G
not present in PGA gain options.....
Even though different set of resistors are connected/disconnected to get different gains of PGA when configured, it is not possible to select which resistor has to be connected in the input side/feedback side using registers, so we can't get any gain factors apart from whatever Component configuration window is showing.
Best way is to use external resistors as suggested by dana.
You can select the input side R as well as the output side. Limited though.