OK. So I have amended the zorro.mq4 file, but zorro seems to be ignoring it. Code as follows:

string assetFix(string Asset)
{
if(Asset == "XAGUSD") return(".SILVER");
if(Asset == "XAUUSD") return(".GOLD");
if(Asset == "GER30") return("DE30");
if(Asset == "NAS100") return("US500");
if(Asset == "SPX500") return("USTEC");
if(Asset == "USOil") return("WTI");
// replace asset name directly (example)
// if(Asset =="XAGUSD") return("SILVER");
// if(Asset == "XAUUSD") return("GOLD");

// no direct replacement -> add suffix automatically
string s = Symbol();
if(StringLen(s) > 6 && StringLen(Asset) <= 6) {
s = StringSubstr(s,6,StringLen(s)-6);
Asset = StringConcatenate(Asset,s);
static bool once = true;
if(once) {
Print("Adding ",s," to asset names");
once = false;
}
}
return(Asset);
}

Even with this file saved in the source folder, Zorro cannot find these symbols. Any suggestions?