Formatting a date in collection valuexpression

I have a project report with a column that displays the name, assignee, and due date of the currently active task. I would like to format the due date as partialAtDate to display the day name.

Normally I would add:

valueformat=partialAtdate

valuefield=plannedCompletionDate

but that won't work in this case because there is a valueformat=HTML already

Does anyone know the syntax for this?

The code below works but has the default "atDate" MM/DD/YY

displayname=Active Task & Due Date

listdelimiter=<div>

listmethod=nested(tasks).lists

textmode=true

type=iterate

valueexpression=IF({numberOfChildren}=0,IF({canStart},IF({status}="CPL","",CONCAT({name}," | ",{assignedTo}.{name}," ",{plannedCompletionDate}))))

valueformat=HTML