Here's the basic outline for a transaction filter that checks quantities of further asset issuances:
function filtertransaction() {
var tx = getfiltertransaction();
for (j = 0; j < tx.vout.length; j++) {
if (tx.vout[j].assets) {
for (k = 0; k < tx.vout[j].assets.length; k++) {
if (tx.vout[j].assets[k].type == "issuemore") {
var newqty = tx.vout[j].assets[k].qty;
var oldqty = getassetinfo(tx.vout[j].assets[k].name).issueqty;
if (oldqty + newqty > 0) return "New qty " + newqty + " old qty " + oldqty;
}
}
}
}
}
You'll need to replace the line with if (oldqty + newqty > 0) to reflect whatever rule you want to apply, and whatever error message you want the filter to return if the rule is violated.