XSLT complex copy

I would like to copy an XML file with a XSL sheet. By copying I want "anonymize" my XML file, taking some elements of the XML as a variable.

Base:

<?xml version="1.0" encoding="ISO-8859-15"?>
<root>
    <top>
        <nbpeople>2</nbpeople>
    </top>
    <people>
        <id>45</id>
        <name>MARTIN</name>
        <firstname>JEAN</firstname>
    </people>
    <people>
        <id>98</id>
        <name>DUPONT</name>
        <firstname>Yves</firstname>
    </people>
</root>

result:

<?xml version="1.0" encoding="ISO-8859-15"?>
<root>
    <top>
        <nbpeople>2</nbpeople>
    </top>
    <people>
        <id>45</id>
        <name>people 45</name>
        <firstname>JEAN</firstname>
    </people>
    <people>
        <id>98</id>
        <name>people 98</name>
        <firstname>Yves</firstname>
    </people>
</root>

My real XML file is obviously more complex.
Thank's