"preceding-sibling::<<Node Name>>" can be use to get all the previous siblings.
But to get the just before sibiling syntax is like below
"preceding-sibling::<<Node Name>>[<<count>>]"
Sample XML doc
<Parents>
<Child id="1" name="Yogesh1" mode="1" />
<Child id="2" name="Yogesh2" mode="1" />
<Child id="3" name="Yogesh3" mode="2" />
<Child id="4" name="Yogesh4" mode="2" />
<Child id="5" name="Yogesh5" mode="2" />
</Parents>
Sample XSLT Template for preceding-sibling
<xsl:template match="Child">
<xsl:if test="@mode != preceding-sibling::Child[1]/@mode">
<xsl:value-of select="Change in mode Attribute" />
</xsl:if>
Name:<xsl:value-of select="@name" />
Id:<xsl:value-of select="@id" />
</xsl:template>