SOURCE

function strInsert(str, length) {
   let reg = new RegExp("\\w{1," + length + "}", "g");
   let ma = str.match(reg);
   return ma.join(":") ; 
}

console.log(strInsert("046e489743baed858c8a79868482bb0ee7c2c8665c4d433324f27da60af8f97706cadee9e26600dc34636eba1ef518819492b189ead85419a1de9db7984accedf6", 2));