XML Parsing in OS X Terminal for MobileConfig file

I am working on generating (actually editing) a mobileconfig file (aka iOS profile, XML) via bash script.

The script fetch data from a MS Database and has now to inject/replace this data in my mobileconfig file (XML).

The XML file has the following structure:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://ift.tt/vvUEPL">
<plist version="1.0">
<dict>
    <key>PayloadContent</key>
    <array>
        <dict>
            <key>Host</key>
            <string>outlook.office365.com</string>
            <key>MailNumberOfPastDaysToSync</key>
            <integer>7</integer>
            <key>Password</key>
            <string>ActiveSyncPassword</string>
            <key>PayloadDescription</key>
            <string>Configures an Exchange account</string>
            <key>PayloadDisplayName</key>
            <string>Exchange ActiveSync</string>
            <key>PayloadVersion</key>
            <integer>1</integer>
            <key>SSL</key>
            <true/>
            <key>UserName</key>
            <string>xxxxxxx@xxx.com</string>
            <key>disableMailRecentsSyncing</key>
            <false/>
        </dict>
        <dict>
            <key>AutoJoin</key>
            <true/>
            <key>EncryptionType</key>
            <string>WPA</string>
            <key>HIDDEN_NETWORK</key>
            <true/>
            <key>IsHotspot</key>
            <false/>
            <key>Password</key>
            <string>WEPWPAWPSPEAPTLS</string>
            <key>PayloadType</key>
            <string>com.apple.wifi.managed</string>
            <key>PayloadVersion</key>
            <real>1</real>
            <key>ProxyType</key>
            <string>None</string>
            <key>SSID_STR</key>
            <string>SSID</string>
        </dict>
        <dict>

I would like to replace the WiFi Password but also ActiveSync "Password" fields between the < string> < /string> using any native (xmllint, sed) or non-native tool.

Can anyone please help ?