This can easily be done in two ways.

If the skin package has html and .xml files included, edit the .xml file in NotePad:
   <Object>
      <Token>[USER]</Token>
      <Settings>
         <Setting>
            <Name>CssClass</Name>
            <Value>whatever</Value>
         </Setting>
         <Setting>
            <Name>Text</Name>
            <Value>Apply</Value>
         </Setting>
      </Settings>
   </Object>

Then re-parse the skin package.

If the skin package has no html and .xml files, edit the skin .ascx files in NotePad:
<dnn:USER runat="server" id="dnnUSER" CssClass="whatever" Text="Apply" />
In this case it's not necessary to re-parse the skin.

Only change the Text="" part.