HowTo append string to existing value when updating in process step

I have a process step using the HandleObject-Update component to update a bunch of datasets *1.  Using the val_ColumnName Jobparameter, I can set a fixed value, let's just say 

value = "New_Text"

How can I tell the process step to APPEND the fixed value to existing value, so that in the end the column-value of each dataset would be "Old_Text New_Text"

Edit: 

* that are linked to my BaseObject, but not the BaseObject itself