いろいろ試行錯誤いたしまして、以下のJavascriptで解決しました。
構造上問題がおきそうな点がありましたらご指摘頂けますと非常にうれしいです。
window.onload = function onLoad() {
var Eyear = document.getElementById("dt:ey");
var EYop = document.getElementById("dt:ey").options;
var EYval = EYop.item(Eyear.selectedIndex).value;
document.getElementById("data:3:y").value = EYval;
var EY2 = document.getElementById("data:3:y");
EY2.setAttribute("onchange", "EY3()");
var Emon = document.getElementById("dt:em");
var EMop = document.getElementById("dt:em").options;
var EMval = EMop.item(Emon.selectedIndex).value;
document.getElementById("data:3:mon").value = EMval;
var EM2 = document.getElementById("data:3:mon");
EM2.setAttribute("onchange", "EM3()");
var Eday = document.getElementById("dt:ed");
var EDop = document.getElementById("dt:ed").options;
var EDval = EDop.item(Eday.selectedIndex).value;
document.getElementById("data:3:d").value = EDval;
var ED2 = document.getElementById("data:3:d");
ED2.setAttribute("onchange", "ED3()");
var Ehour = document.getElementById("dt:eh");
var EHop = document.getElementById("dt:eh").options;
var EHval = EHop.item(Ehour.selectedIndex).value;
document.getElementById("data:3:h").value = EHval;
var EH2 = document.getElementById("data:3:h");
EH2.setAttribute("onchange", "EH3()");
var Emin = document.getElementById("dt:emin");
var EMiop = document.getElementById("dt:emin").options;
var EMival = EMiop.item(Emin.selectedIndex).value;
document.getElementById("data:3:min").value = EMival;
var EMi2 = document.getElementById("data:3:min");
EMi2.setAttribute("onchange", "EMi3()");
var Syear = document.getElementById("dt:sy");
var SYop = document.getElementById("dt:sy").options;
var SYval = SYop.item(Syear.selectedIndex).value;
document.getElementById("data:4:y").value = SYval;
var Smon = document.getElementById("dt:sm");
var SMop = document.getElementById("dt:sm").options;
var SMval = SMop.item(Smon.selectedIndex).value;
document.getElementById("data:4:mon").value = SMval;
var Sday = document.getElementById("dt:sd");
var SDop = document.getElementById("dt:sd").options;
var SDval = SDop.item(Sday.selectedIndex).value;
document.getElementById("data:4:d").value = SDval;
var YY = document.getElementById("data:19:stock");
YY.setAttribute("placeholder", "予約上限");
var YY2 = document.getElementById("price-form-19");
YY2.setAttribute("placeholder", "料金");
}
// -->function EY3() {
var E2year = document.getElementById("data:3:y").value;
document.getElementById("dt:ey").value = E2year;
}function EM3() {
var E2month = document.getElementById("data:3:mon").value;
document.getElementById("dt:em").value = E2month;
}function ED3() {
var E2day = document.getElementById("data:3:d").value;
document.getElementById("dt:ed").value = E2day;
}function EH3() {
var E2hour = document.getElementById("data:3:h").value;
document.getElementById("dt:eh").value = E2hour;
}function EMi3() {
var E2min = document.getElementById("data:3:min").value;
document.getElementById("dt:emin").value = E2min;
}