Automation update (by only adding, not deleting) in another table

To make sure I understand, your third table is basically a Junction/Linking table between Campaign and Asset? So there should be a single record for each Campaign-Asset combination?

If this is the case, you can use a Search Records in your automation, see if a record with the two IDs exist already, and skip the creation on this condition.

So basically I have two tables: 

In the first one: 
I have the asset name and data, and I can add “used in campaigns” (this is a multiple select option). So imagine that this asset is used in campaign A, I select that one in there (this counts as an update). As soon as this field is updated I have an automation that creates a new record in the Campaign 2025 tab.

So in this example I have this asset that was used in 2 different campaigns
 

Every time I update the Asset tracker tab this creates a new record on the Campaign 25 tab, this way I can add performance fields to check out this particular asset performed on a specific campaign.
 

But, if for some reason I chose the wrong campaign and now need to delete the “annual report” now, it will create another record because that counts as an “update”.

I’ve tried to used the “match criteria” automation, but this does not create a new record, just updates the information.