It might be a bit tricky to get the right trigger for an automation without scripting. If you use the “when record is updated” trigger; note that the automation will be triggered by both having a new record inked and when a linked record is removed, but the trigger will not be able to identify which event happened. Also, the automation will not be able to directly identify which is the new linked record. There are workarounds that involve formula fields and additional automation actions, but they can get tricky.
On the other hand, if you want to write a script, or are willing to hire someone to write a script, what you want could be accomplished with a code. The code could be either an automation script or a script that is run from a button, depending on what is best for your workflows.