For those interested. We copied part of the validation check, and updated with some options to truncate as per the schema.

It can be called with:

set tSC = ##class(User.Hl7RangeCheck).RangeChk(.pRequest)

Include EnsHL7

Class User.Hl7RangeCheck
{ ClassMethod RangeChk(ByRef pMsg As EnsLib.HL7.Message) As %Status
{
#dim pIndex as %Integer = 1
Set tSC=$$$OK , tSC2=$$$OK, tSC1=$$$OK
for 
{
set pSeg = pMsg.GetSegmentAt(pIndex)
quit:($ZSTRIP(##class(%String).LogicalToDisplay(pSeg), "<>W" ) = "") quit:(pSeg.Name = "") //$$$ERROR($$$EnsErrGeneral, "Cannot validate segment schemas without a segment name. Unable to validate segment "_$get(pSegNum)_".")
set hasSegNum = 1 - ($get(pSegNum)="")
quit:(pSeg.DocTypeCategory = "") //$$$ERROR($$$EnsErrGeneral, "Cannot validate segment schemas without a category. Unable to validate segment "_$S(hasSegNum:pSegNum_":",1:"")_pSeg.Name_".")
quit:($get($$$vaSchemaGbl(pSeg.DocTypeCategory, "SS", pSeg.Name)) = "") //$$$ERROR($$$EnsErrGeneral, "Unable to retrieve the schema to validate segment against. Unable to validate segment "_$S(hasSegNum:pSegNum_":",1:"")_pSeg.Name_".")
set schema = $$$vaSchemaGbl(pSeg.DocTypeCategory, "SS", pSeg.Name)
for fieldNum=1:1:$listlength(schema)
{
quit:(fieldNum > pSeg.Count)
set fieldDat = pSeg.GetValueAt(fieldNum, pSeg.Separators, .tSC2)
if ($$$ISERR(tSC2))
{
set tSC = $$$ADDSC(tSC, $$$ERROR($$$EnsErrGeneral, "Unable to retrieve field "_fieldNum_" from segment "_$S(hasSegNum:pSegNum_":",1:"")_pSeg.Name_"."))
quit ; can only continue with this field if no error in getting it
}
set fieldSchema = $listget(schema, fieldNum)
if '(((pSeg.Name = "MSH") || (pSeg.Name = "BHS") || (pSeg.Name = "FHS")) && ((fieldNum = 1) || (fieldNum = 2)))
{
set dat = $tr(fieldDat, pSeg.Separators, "") ; remove separators from field
}
else 
{
set dat = fieldDat
}
set data = (dat '= "") ; is anything left?
if (data)
{
//if not data structures, components, subcomponents, datatypes, and/or code tables
if ($listget(fieldSchema, 1) = "")
{ set len = $length(fieldDat)
if (($listget(fieldSchema, 4) '= "") && (len > $listget(fieldSchema, 4))) ; over length restriction
{
if '(((pSeg.Name = "MSH") || (pSeg.Name = "BHS") || (pSeg.Name = "FHS")) && (fieldNum = 2))
{
for rep=1:1:($length(fieldDat, pSeg.RS))
{
if ($length($p(fieldDat, pSeg.RS, rep)) > $listget(fieldSchema, 4))
{ 
set tSC = pMsg.SetValueAt(..Truncate(pMsg.GetValueAt(pSeg.Name_":"_fieldNum_"("_rep_")"),$listget(fieldSchema, 4)) , pSeg.Name_":"_fieldNum_"("_rep_")")
}
}
} }
}
else 
{
k info
set info("SegName") = pSeg.Name , info("fieldNum") = fieldNum, info("sep") = pSeg.Separators
set (info("rep"), info("comp"), info("subComp")) = 1
set:(hasSegNum) info("SegNum") = pSegNum
set info("hasSegNum") = hasSegNum if ($listget(fieldSchema, 1) '= "") ; there is a data structure for the field
{
set dataStruct = $listget(fieldSchema, 1)
set tSC = ..ValidateFieldDataStructure(.pMsg,fieldDat, dataStruct, .info)
}
}
}
} set pIndex = pIndex+1
}
return tSC
} ClassMethod ValidateFieldDataStructure(ByRef pMsg As EnsLib.HL7.Message, field As %String, struct As %String, ByRef info) As %Status [ Internal ]
{
set tSC = $$$OK, error = 0
set category = $p(struct, ":", 1)
set dataStruct = $p(struct, ":", 2)
quit:((category = "") || (dataStruct = "")) $$$ERROR($$$EnsErrGeneral, "Cannot find schema for data structure "_struct_". Unable to validate segment "_$S($get(info("SegNum"))'="":info("SegNum")_":",1:"")_info("SegName")_" field "_info("fieldNum")_" against this structure.")
set structure = $get($$$vaSchemaGbl(category, "DT", dataStruct))
quit:('$data(structure)) $$$ERROR($$$EnsErrGeneral, "Cannot find schema for data structure "_struct_". Unable to validate segment "_$S(info("hasSegNum"):info("SegNum")_":",1:"")_info("SegName")_" field "_info("fieldNum")_" against this structure.") if '(((info("SegName") = "MSH") || (info("SegName") = "BHS") || (info("SegName") = "FHS")) && (info("fieldNum") = 2))
{
for info("rep") = 1:1:$length(field, $$$RSSEP(info("sep")))
 {
set repeat = $piece(field, $$$RSSEP(info("sep")), info("rep"))
for info("comp")=1:1:$length(repeat, $$$CSSEP(info("sep")))
{
quit:(info("comp") > $listlength(structure))
set component = $piece(repeat, $$$CSSEP(info("sep")), info("comp"))
set dat = $tr(component, $$$SSSEP(info("sep"))) ; remove separators from field
set data = (dat '= "") ; is anything left?
if (data)
{
set len = $length(component)
if (($listget($listget(structure, info("comp")),3)'="") && (len > $listget($listget(structure, info("comp")),3))) ; over length restriction
{ 
set tSC = pMsg.SetValueAt(..Truncate(component,$listget($listget(structure, info("comp")),3)), info("SegName")_":"_info("fieldNum")_"("_info("rep")_")"_"."_info("comp"))
}
}
}
}
}
Return tSC
} ClassMethod Truncate(pString As %String, pNum As %Integer) As %String
{
#dim tString As %String = pString If ($LENGTH(pString) > pNum)
{
Set tString = $EXTRACT(pString,1,pNum)
} Return tString
} }