A script will let you do that.
Something like this should get you going (you’ll have to adjust, according to your metadata structure):
var myMeta = new ActiveXObject("MetadataLib.MetaFile");
myMeta.LoadFromFile(Watch.GetMetadataFileName());
var myGroup = myMeta.Job().Group(0);
for(var myDocs = new Enumerator(myGroup); !myDocs.atEnd(); myDocs.moveNext()) {
var myDoc = myDocs.item();
var myField = myDoc.FieldByName("myField").replace(/##/g,"").replace(/\n/g," ");
myDoc.Fields.Add("myField",myField);
}
myMeta.SaveToFile(Watch.GetMetadataFileName());
The script removes the ## characters and replaces new line characters with a space.