> Is it possible to place an <xsl:attribute> as a child of a <xsl:copy- 
> of select="."> 

No but you can place it as a child of xsl:copy, which is what you want
to do here.

  Or do I need to  
  enumerate xsl:element/xsl:attribute for all elements and attributes  
  possible in my input?

No you can just use @*, something like

<xsl:copy>
 <xsl:copy-of seelct="@*"/>
 <xsl:attribute name="new">stufff


to give you an element with the same name  and attributes as you had
before, plus a new attribute new=...

David

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