Resolution:
A unique ID can be generated using the attached file (Filename: GenerateUUID.zip).
The instructions to use this are:

- Unzip the attached file into the $ASG_HOME/projects/ASG_DefaultImplementation/DefaultImplementation/Rules/CustomStages/ directory. A new dir "GenerateUUID/" with one entry "InsertInLifeCycle.rule" should be created.

- Open the project in ASG Studio and recompile the asg_core.ear file. Be sure to make a backup of the existing one first.

- add an OperationFeature with value "GenerateUUID" to the required Facade Operation

- in all the mappers a new element in the context XML document with key="ms:uuid" should be seen

- The value may be extracted using the XPath.

<xsl:variable name="context">
<!-- xsl:if test="/transformation/context/@size>0"-->
<xsl:copy-of select="document(/transformation/context/@href)/*"/>
<!--/xsl:if-->
</xsl:variable>
<xsl:variable name="uid">
<xsl:if test=" exists($context//c:entry[@key='ms:uuid'])">
<xsl:copy-of select="$context//c:entry[@key='ms:uuid']"/>
</xsl:if>
</xsl:variable>

How to generate a Unique ID in TIBCO API Exchange Gateway(APIX-G)?