You can use the following:

<assign property='target.Source' value='source.Source' action='set'/>

This applies to any body property. Notice the difference between source (lowercase 's') representing the source message and Source (uppercase 'S') representing the body property. The more general syntax would be:

<assign property='target.BodyPropName' value='source.BodyPropName' action='set'/>

If you are using the graphical editor, you add a set action and type in the Property and Value.

You can override the OnConstructReply method from EnsLib.HL7.Service.Standard. The following worked for me.

Class DC.CustomACKBS Extends EnsLib.HL7.Service.TCPService
{

Method OnConstructReply(Output pReplyDoc As EnsLib.EDI.Document, pOriginalDoc As EnsLib.EDI.Document, ByRef pReplyCode As %String, ByRef pSC As %Status, pEarlyAck As %Boolean) As %Status
{
    Set pReplyDoc=##class(EnsLib.HL7.Message).%New()
    Set pReplyDoc.DocType="2.4:ACK"
    Set MSHStr="MSH|^~\&|EnsembleHL7|ISC|ARiM Server|ROWA|"_$REPLACE($REPLACE($ZDATETIME($HOROLOG,8,1),":",""), " ","")_"||ACK|"_pOriginalDoc.GetValueAt("MSH:10")_"|P|2.3"
    Set MSHSeg=##class(EnsLib.HL7.Segment).ImportFromString(MSHStr,.tSC,pOriginalDoc.Separators)
    Set MSAStr="MSA|AA|"_pOriginalDoc.GetValueAt("MSH:10")
    Set MSASeg=##class(EnsLib.HL7.Segment).ImportFromString(MSAStr,.tSC,pOriginalDoc.Separators)
    Set tSC=pReplyDoc.SetSegmentAt(MSHSeg,1)
    Set tSC=pReplyDoc.AppendSegment(MSASeg)

    Quit tSC
}

}

Your Business Operation has a setting called Throttle Delay. You could set this to the number of milliseconds you would like to delay before processing the next message.

https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls...

You should create a custom schema with a custom ADT_A01 message type and structure. Documentation has a section on Creating a New Custom Schema.

Then, you may use that custom schema as you would any of the standard schemas. So, you can use your custom ADT_A01 message structure (with the MRG segment) as the target in your data transformation.

To use the Euro symbol € as an example, it is a character in UTF-8. However, it is not a character in Latin1. Your Business Service uses the Default Char Encoding setting to read the message, so it does not read the Euro symbol as you would expect. Changing the Default Char Encoding to "unicode utf-8" would allow the Business Service to read that character as you would expect.

When you output your message, nothing in the message has actually changed (unless you have done some sort of Data Transformation). So, when you open the text editor, which uses UTF-8, you are able to see the Euro symbol again.

Have you tried GetContentArray() from EnsLib.HL7.Message? Then you could do something similar to Testing Virtual Property Paths in the Terminal. For example,

 ClassMethod PrintPropertyPaths()
{
 set string="MSH|^~\&|MIHIN PATIENT GEN|1.2.3.4.5.9.99.999.9999.1004||2.16.840.1.113883.3.1481|20200103000000+0000||ADT^A01^ADT_A01|1092|P|2.6|1091|||||||||Windward General Hospital"_$C(13,10)_
            "EVN||20200110000000+0000|||||1.2.3.4.5.9.99.999.9999.1004"_
            "PID|1|3170|44c8a6bba5c743538e476a813256959b^^^^CKS~000003170^^^^SS||Santana^Pearl||19900609|F||2054-5^Black or African American^HL70005|364 NE Oak Circle^^Trenton^MI^48183||||||||000003170|||N^Not Hispanic or Latino^HL70189|||||||20200110000000+0000|N"_$C(13,10)_
            "PD1|||Windward General Hospital^^^^^^^^^1.2.3.4.5.9.99.999.9999.1004|9999992221^Johnston^Karl^^^^^^^^^^NPI^^^^^^^^MD"_$C(13,10)_
            "PV1|1|I|^^67^1.2.3.4.5.9.99.999.9999.1004||||9999992221^Johnston^Karl^^^^^^^^^^NPI||||||||||||17a5e3aa59a34ad5af017998278a5eb5||||||||||||||||||&HOME^20200110000000+0000|||||||20200103000000DG1|1||Z34.90^Normal pregnancy^I10||20200103000000+0000|F|^Become_Pregnant"_$C(13,10)_
            "IN1|1|1772^STATE HEALTH PLAN|1027|MEDICAID||||||||||||Santana^Pearl^Gladys|||364 NE Oak Circle^^Trenton^MI^48183"_$C(13,10)
 set target=##class(EnsLib.HL7.Message).ImportFromString(string,.status)
 if 'status {do $system.Status.DisplayError(status) quit}
 set target.DocType="2.6:ADT_A01"
 
 do target.GetContentArray(.propertyPaths,, target.DocType)
 for i=1:1:propertyPaths {
   for j=1:1:propertyPaths(i) {
     w i, ".", j, propertyPaths(i,j, "name"), !
   }
 }
}

I see two things here. First, in your Data Transformation, since PIDgrpgrp() repeats, you will need to specify a repetition in the parenthesis like PIDgrpgrp(1) for the first repetition.

<assign value='##class(CUSTOM.Training.Functions).DateTime(source.{PIDgrpgrp(1).PIDgrp.PID:7.1})' property='target.{PID:7.1}' action='set' />

Then, in your DateTime method, you will need to return the year. For example, if the DateTime was formatted YYYYMMDD:

ClassMethod DateTime(DateTime As %Integer)
 {
   Set Year = $EXTRACT(DateTime,1,4)
   Quit Year
 }

Replace HL7.{propertypath} with Document.{propertypath}. For example,

Document.{MSH:9}

You will not have virtual property completion to refer to the segments/fields in an HL7 message, but you can continue to build your conditions in your HL7 message router and paste them in.