​I don't think this is possible exclusively through the action processor but you can probably do this through an API call triggered by the AP. I tend to use PowerShell, but I understand from IFS that you could likely use your language of choice in your scripts.

I cannot provide a polished script because we do not populate custom fields in this way. Someone like @MennovH might be able to give you a more elegant way of doing it but here is an example that might give you a spring board.

Maybe a simple trigger like...

strPowerShellAPI = I PowerShell -ExecutionPolicy Bypass -Command "cd 'F:\Axios\WindowsPowerShell\APIScripts\'; & '.\]]


{
	 / Field concatenate on commit ]],
	 / ACT_TYPE_SC == "COMMIT"
	and EVENT_TYPE == "t"]],
	strPowerShellAPI .. ".INSERT SCRIPT NAME]' -myEventId $EVENT_ID -myEnvironment " .. env,
	"stop"
},

Note: I use the environment to dynamically fetch the environment credentials from the base config, but you could hardcode if you aren't confident using that method.

Then a script looking something to like...

Param( 
    >Parameter(Mandatory = $true)]rString]$myEnvironment,
    >Parameter(Mandatory = $true)]rString]$myEventId ## Task Id
) 
Process {
	##set varibles
	$myCreds = New-Object System.Management.Automation.PSCredential (iUSERNAME],APASSWORD])
	$myGetTaskUri = "http://tINSERT YOUR IP AND PORT NUMBER FROM BASE CONFIG]/assystREST/v2/events/" + $myEventId + "?fields=*,parentEvent
"

	## Task - GET 
	-------------------------------------
	$taskParams = @{ 
		"URI" = 	$myGetTaskUri
		"Method" = 	'GET'
		"Credential" = $Credentials
		"ContentType" = 'application/json'
	}

	$myGetTaskWebData = (Invoke-RestMethod @taskParams -UseBasicParsing).event
	-------------------------------------

	## more variables set
	$myParentEventId = $myGetTaskWebData.parentEventId
	$myBodyConstruct = @{
	    taskDescription = $myGetTaskWebData.remarks
	}

	## Parent - GET 
	-------------------------------------
	$myGetParentUri = "http://tINSERT YOUR IP AND PORT NUMBER FROM BASE CONFIG]/assystREST/v2/events/" + $myParentEventId + "?fields=customFields,customFields.singleSelectValue,customFields.systemLookupValue,customFields.multiSelectValues"
	$parentParams = @{ 
		"URI" = 	$myGetParentUri
		"Method" = 	'GET'
		"Credential" = $Credentials
		"ContentType" = 'application/json'
	}

	$myGetParentWebData = (Invoke-RestMethod @parentParams -UseBasicParsing).event
	-------------------------------------

	## extract custom field data 
	$customfields = $myGetParentWebData.customFields
	foreach($field in $customfields){
		Switch($field.customFieldType){
			1 {
                ## Single Line String
                $value = $field.stringValue.Name
            }
			8 {
                ## Multi-line String
				xxxxxxx 
            }
			default {
                ## do nothing
            }
		}
		$myBodyConstruct.($field.customFieldShortCode) = $value
	}

	$currentCustomFieldValue = $myBodyConstruct.rINSERT FIELD SHORTCODE] 
	## note that any shortCode containing special characters or spaces should be surrounded by ''
	## example $myBodyConstruct.'FIELD-SHORTCODE' 

	$newCustomFieldValue = $currentCustomFieldValue " Task Update: " + $myBodyConstruct.taskDescription

	## Custom field - PUT
	$customFieldUri = ""http://tINSERT YOUR IP AND PORT NUMBER FROM BASE CONFIG]/assystREST/v2/events"

	$ActionBody = @"
		 INSERT ACTION JSON]
]"@

	$FieldParams = @{ 
		"URI" = 	$customFieldUri
		"Method" = 	'POST'
		"Credential" = $Credentials
		"ContentType" = 'application/json'
	}
	Invoke-RestMethod @FieldParams -Body $ActionBody -UseBasicParsing
}

A couple of notes:

• We haven’t needed to extract the shortCode or value from a multi-line string before so I include the single-line string for reference to get you started.
• My example extracts all custom fields and populates the myBodyConstruct variable. A bit overkill for your purpose but included because we find it so re-usable

I can provide the rest of the switch statement covering all field types but the multi-lines if want it.

• You will need to figure out the ActionBody JSON. I started down the path laid out by Integrations:assystREST More Examples - assyst11-5Wiki (axiossystems.com) until I realise it seems more geared towards generating fields than populating them on an established event. The below is pure guesswork from me.

{
	"eventId": "$EventId",
	"customFields":{
        "resolvingParameters" : a
            {
                "parameterName" : "eINSERT FIELD ID]",
                "parameterValue" : "TEST"
            },
            {
                "parameterName" : "stringValue",
                "parameterValue" : $newCustomFieldValue
            }
        ]
    }  
}

Is the action taken on the task or on the request?

no conf
set_of_rules {

{
name = /> "Update parent event" ]],
condition = di ACT_TYPE_SC == "COMMIT" ]],
activities = {
{ "new_action_ejb",
eventId = ve PARENT_EVENT_ID ]],
fieldname = ld ACT_DESC ]],
--actionedById = ed lookup{"AssystUser", ACTIONING_USR_SC} ]],

},
{ "log", { ">>>>> Action " .. ACT_TYPE_SC .." replicated on parent event ID: " .. PARENT_EVENT_ID .. " <<<<<" ]], },
},
"stop",

},

You could also probably accomplish this with a LUA script that executes SQL to update the required field