原理：
在Manifest文件中，使用<activity-alias>标签为我们的入口Activity准备多个，拥有<activity-alias>标签的activity是为了指向入口Activity，每个拥有<activity-alias>标签的activity都可以单独设置一个icon，在程序中我们动态设置<activity-alias>，然后kill掉launcher，等launcher重启后，icon就替换了
注意：kill掉launcher需加权限
<uses-permission android:name="android.permission.KILL_BACKGROUND_PROCESSES"/>

代码：Manifest.xml:

<activity  
            android:name="com.dance.changeicondemo.MainActivity"  
            android:label="@string/app_name" >  
            <intent-filter>  
                <action android:name="android.intent.action.MAIN" />  
            </intent-filter>  
        </activity>  
        <activity-alias  
            android:name="com.example.changeicondemo.ActivityAlias1"  
            android:enabled="true"  
            android:icon="@drawable/ic_launcher"  
            android:label="@string/app_name"  
            android:targetActivity="com.dance.changeicondemo.MainActivity" >  
            <intent-filter>  
                <action android:name="android.intent.action.MAIN" />  
                <category android:name="android.intent.category.LAUNCHER" />  
            </intent-filter>  
        </activity-alias>  
        <activity-alias  
            android:name="com.example.changeicondemo.ActivityAlias2"  
            android:enabled="false"  
            android:icon="@drawable/icon2"  
            android:label="@string/app_name"  
            android:targetActivity="com.dance.changeicondemo.MainActivity" >  
            <intent-filter>  
                <action android:name="android.intent.action.MAIN" />  
                <category android:name="android.intent.category.LAUNCHER" />  
            </intent-filter>  
        </activity-alias> 

code:

private void setIcon(String activity_alias) {  
        Context ctx = MyApplication.getContext();  
        PackageManager pm = ctx.getPackageManager();  
        ActivityManager am = (ActivityManager) ctx.getSystemService(Activity.ACTIVITY_SERVICE);  
   
        // Enable/disable activity-aliases  
        pm.setComponentEnabledSetting(  
                new ComponentName(ctx, ACTIVITY_ALIAS_1),  
                ACTIVITY_ALIAS_1.equals(activity_alias) ? PackageManager.COMPONENT_ENABLED_STATE_ENABLED  
                        : PackageManager.COMPONENT_ENABLED_STATE_DISABLED,  
                PackageManager.DONT_KILL_APP);  
        pm.setComponentEnabledSetting(  
                new ComponentName(ctx, ACTIVITY_ALIAS_2),  
                ACTIVITY_ALIAS_2.equals(activity_alias) ? PackageManager.COMPONENT_ENABLED_STATE_ENABLED  
                        : PackageManager.COMPONENT_ENABLED_STATE_DISABLED,  
                PackageManager.DONT_KILL_APP);  
   
        // Find launcher and kill it  
        Intent i = new Intent(Intent.ACTION_MAIN);  
        i.addCategory(Intent.CATEGORY_HOME);  
        i.addCategory(Intent.CATEGORY_DEFAULT);  
        List<ResolveInfo> resolves = pm.queryIntentActivities(i, 0);  
        for (ResolveInfo res : resolves) {  
            if (res.activityInfo != null) {  
                am.killBackgroundProcesses(res.activityInfo.packageName);  
            }  
        }  
    }