This is more of an implementation question than code review.
I am currently using the 'clone' standard button that triggers changes on the new cloned record. However, I also have to mark the old record as having been cloned, or I'm looking to update a field in some way on the record.
I am aware that Trigger.oldMap() can be used for looking at old record values, but it can't update the old record field and give me a 'read only' error.
What is the best way to do this if not in the trigger I've already written?