The FCOM states that the approach procedure cannot be modified from FAF to MAPt, so adjusting altitudes to compensate the final segment for temp is not possible. Our company policy describes this as the reason LNAV/VNAV minima cannot be used when below the minimum temp. FCOM also says a vertical selected mode is available and consequently the minima will change to the published LNAV only minima. ( That's our company guidance anyway )