Bograt,
You can use that QNH for a local QNH. However for instrument approaches. AIP ENR 1.5 -33 para 5.3.1 (QNH sources) specifies
a. the actual aerodrome QNH from an approved source, or
b. the forecast Terminal QNH, or
c. the forecast area QNH.
No mention of local QNH so we are back to forecast area QNH as the only applicable QNH.