Custom work item attribute values not exported in Process Template?

I am trying to create a reusable RTC Process Template that subsequently is part of a CLM Lifecycle project.  This Process Template has customized work items with an additional custom attribute. We'll call the attribute XYZ.  In my process template, when exported, I can see all of the work item entities in the 26.xml.  Each item will look something like:

I can subsequently recreate the work items in a new project instance created from this process template. However, it does not capture any of the custom attributes values.  If you see in the above, there is no <rtc_cm:XYZ> tag.

As a test, I manually updated the 26.xml so that it contained something like:

        <rtc_cm:task rdf:ID="item180">
            <rtc_cm:XYZ>4.4.4.4.4</rtc_cm:XYZ>

            <rtc_cm:filedAgainst rdf:resource="${filedAgainst:Category}"/>
            <dc:description>Long custom description</dc:title>
            <rtc_cm:plannedFor rdf:resource="${plannedFor:Iteration}"/>
            <rtc_cm:com.ibm.team.workitem.linktype.parentworkitem.parent rdf:resource="#item171"/>
        </rtc_cm:task>

Then updated the process template archive file, importing into RTC.  Created another CLM/RTC project based on the CLM template that uses this underlying RTC process template. Then went to create work items based on template... And it still did not carry over the custom attribute values. To be clear, the custom attributes exist on the work items, but they have no values assigned.  Also to note, a default value would not apply as every work item needs a unique, specific value.

Is what I'm trying to do possible?

If so, what am I doing wrong?