Just a suggestion. You are using PtrList of entries (https://develop.openfoam.com/Community/avalanche/blob/module-1712/applications/utilities/releaseAreaMapping/releaseAreaMapping.C#L65).

If fields were a plain dictionary entry instead, you could walk easily and also benefit from using other dictionary expansions. For example,

base { ... }
releaseArea1 { ... }
releaseArea2 { ... }

and then later

fields
{
    hentrain
    {
        regions
        {
            $base;
            $releaseArea1;
        }
    }

    h
    {
        default h0 [0 1 0 0 0 0 0] 1e-5;

        regions
        {
            $releaseArea1;
        }
    }
}

Or place the information in a separate file and use and #include within each regions dictionary.