No, you will most certainly end up with inconsistencies in your database. "If you would change a product to be tracked now, what even should happen with the old moves? What's with the stuff that might be in stock already?" is what Odoo wonders, hence the Invalid Operation error.

Without getting deeply involved with stock movements and forcefully setting the flag on the product, i.e. via an database operation, you will have to archive the product and create a new one.