I don't think an ILS will help with that.
It can do - ILS cat. IIIb allows no decision height and as little as 50m visibility - but - well - Modlin only has a cat. I ILS at the moment and will probably never have better than a cat. II one.
Interestingly, the Boeing 737 isn't certified for anything more than cat. IIIa.
In the last few weeks Modlin arriving and departing flights have been diverted to Okęcie because of severe fog problems.
It's a problem all over Poland at the minute - Poznan-Lawica has been closed on numerous occasions too. The fog has been shockingly bad - several times, I've found myself with less than 200m visibility when driving.