Add a new feature? No. Add a column to the database? No. Add another way to lookup a data item? No. Add a new query param to the API? No. No no no no. A quick rule to follow when you want your project to keep a tight scope, to remain scalable and easy to maintain, is to say no to everything.
Feature creep can be subtle, the simple change of making an attribute required in your data model leads to a slew of other new "expected" behaviors.