Add variable as attribute to subnodes of a XML in TSQL - sql-server

Question

I am trying to add the value of a pre-defined variable to each individual subnode of my XML. I found this question SO Question and its answer, which looks pretty neat to me.
However, I can't use the variable #modification_time as an input for the attribute.
DECLARE #xml XML=
N'<ContentTemplate>
<Tab Title="Lesson">
<Section Title="Lesson Opening" />
<Section Title="Lesson/Activity" />
</Tab>
<Tab Title="Wrap Up and Assessment">
<Section Title="Lesson Closing" />
<Section Title="Tracking Progress/Daily Assessment" />
</Tab>
<Tab Title="Differentiated Instruction">
<Section Title="Strategies - Keyword" />
<Section Title="Strategies – Text" />
<Section Title="Resources" />
<Section Title="Acceleration/Enrichment" />
</Tab>
<Tab Title="District Resources">
<Section Title="Related Content Items" />
<Section Title="Other" />
</Tab>
</ContentTemplate>';
I can't figure out if it's possible and how to add the variable value to the subnode.
DECLARE #modification_time nvarchar(30);
SET #modification_time = FORMAT(CURRENT_TIMESTAMP,'yyyy-MM-ddTHH:mm:ss' ) ;
SET #xml=#xml.query(
'<ContentTemplate>
{
for $t in /ContentTemplate/Tab
return
<Tab Title="{$t/#Title}" PortletName="CommunitiesViewer" ModificationTime="VariableValuehere" >
{$t/*}
</Tab>
}
</ContentTemplate>');
SELECT #xml