[xsl] overwriting certain blocks of output - two queries

[Rahil <qamar_rahil@xxxxxxxxxxx>]

Hi

I want to overwrite certain blocks of output (o/p) that I obtain from my 
first.xsl file with the results from second.xsl.

The process flow is such :

input.xml (call to first.xsl) --> first.xsl (some processing) --> 
first.xml (use saxon:next-in-chain) -->second.xsl (target certain o/p 
areas of first.xml) -->second.xml (final result)

first.xml looks such:

<Top>
<Parts>
   <A>
        <Class id="123" type="none">Parts</Class>
        <Value id="345" type="CODED_TEXT">Handle</Value>
   </A>
   <B>
        <Class id="none" type="Property">Handle</Class>
        <Value id="234" type="Property">hasProperty Bolt</Value>
   </B>
</Parts>
<Components>
    <A>
        <Class id="123" type="none">Components</Class>
        <Value id="345" type="CODED_TEXT">Car</Value>
   </A>
   <B>
        <Class id="none" type="none">Not Present</Class>
    </B>
</Components>
</Top>

Now second.xsl processes first.xml by pulling out all B/Class[.='Not 
Present']. Then it does some stuff and gets some results so that I 
finally have second.xml looking like this:

<Top>
<Parts>
   <A>
        <Class id="123" type="none">Parts</Class>
        <Value id="345" type="CODED_TEXT">Handle</Value>
   </A>
   <B>
        <Class id="none" type="Property">Handle</Class>
        <Value id="234" type="Property">hasProperty Bolt</Value>
   </B>
</Parts>
<Components>
    <A>
        <Class id="123" type="none">Components</Class>
        <Value id="345" type="CODED_TEXT">Car</Value>
   </A>
   <B>
        <Class id="none" type="876">CarLocks</Class>
         <Value id="909" type="Property">hasProperty Mirror</Value>
    </B>
</Components>
</Top>

How do I overwrite certain nodes while preserving the remaining structure?

Also is it possible to overwrite other blocks of first.xml 
retrospectively, say the block Top/Parts/A, if a certain condition is 
met later on ?

Will appreciate any suggestions and help

Thanks
Rahil