[Xposed Framework Modules] Falseclock:
This module fixing external SD card write issue on Android 4.4 KitKat. Module does not have any setting activity. Just enable it in Module tab and restart your phone.

No need to patch platform.xml file.

http://repo.xposed.info/module/kz.virtex.android.sdcardfix

Can be downloaded in Xposed Download tab.

HOW IT WORKS and WHAT FOR?

KitKat No SD card access

If SD card write access not enabled, then no any application without root permission can operate with files on SD Card.

[YOUTUBE]3Jvxp8CvpF0[/YOUTUBE]

KitKat WITH SD Card access

Once mod is enabled - any application without root access can operate with files on SD, including move, copy, delete.

[YOUTUBE]AqmW0Lzh8lE[/YOUTUBE]

Source code for other developers

/*
The MIT License (MIT)

Copyright (c) 2014 by Nurlan Mukhanov aka Falseclock

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

package kz.virtex.android.sdcardfix;

import de.robv.android.xposed.IXposedHookZygoteInit;
import de.robv.android.xposed.XC_MethodHook;
import de.robv.android.xposed.XposedHelpers;

public class XMain implements IXposedHookZygoteInit
{
@Override
public void initZygote(StartupParam startupParam) throws Throwable
{
final Class<?> pms = XposedHelpers.findClass("com.android.server.pm.PackageManagerService", null);

XposedHelpers.findAndHookMethod(pms, "readPermission", "org.xmlpull.v1.XmlPullParser", "java.lang.String", new XC_MethodHook()
{
protected void afterHookedMethod(MethodHookParam param) throws Throwable
{
String permission = (String) param.args[1];

if (permission.equals("android.permission.WRITE_EXTERNAL_STORAGE")) {
Class<?> process = XposedHelpers.findClass("android.os.Process", null);
int gid = (Integer) XposedHelpers.callStaticMethod(process, "getGidForName", "media_rw");
Object mSettings = XposedHelpers.getObjectField(param.thisObject, "mSettings");
Object mPermissions = XposedHelpers.getObjectField(mSettings, "mPermissions");
Object bp = XposedHelpers.callMethod(mPermissions, "get", permission);
int[] bp_gids = (int[]) XposedHelpers.getObjectField(bp, "gids");
XposedHelpers.setObjectField(bp, "gids", appendInt(bp_gids, gid));
}
}
});
}

private static int[] appendInt(int[] cur, int val)
{
if (cur == null) {
return new int[]
{ val };
}
final int N = cur.length;
for (int i = 0; i < N; i++) {
if (cur[i] == val) {
return cur;
}
}
int[] ret = new int[N + 1];
System.arraycopy(cur, 0, ret, 0, N);
ret[N] = val;
return ret;
}
}