To answer your first question refer FCTM
PR-NP-SOP-160 p15/30. It describes how VREF = VLS in CONF FULL. This why abnormal landing VAPP computations start with VLS conf full add delta VREF and then we change the MCDU back to CONF 3. ( however I don’t think this does anything other than changing the VLS value on the PERF APP page. VAPP can’t change as you manually entered it.)
The computers take the landing configuration from the GPWS LANDING FLAP SELECTION. So providing it is set to CONF 3 the GS Mini should be available ( F Speed disappears from speed tape on selection of landing CONF ) and Landing memo will correctly show CONF 3.