<xsl:template match="persoonsgegevens[1]">
...
</xsl:template>

I would like to treat all other nodes differently...
   <xsl:template match="persoonsgegevens[?]">
...
</xsl:template>

remember, according to the docs persoonsgegevens[1] is really short for
persoonsgegevens[position() = 1]

position() != 1?
position() <> 1?
not(position() = 1)
position() > 1 ?