This is the most reliable way to apply "high-quality" changes that persist across sessions. :
Disclaimer: This article is for informational and educational purposes only. Modifying game files violates the EA User Agreement. Use save editors at your own risk. The author assumes no responsibility for account suspensions or corrupted data. nfs unbound save editor extra quality
If you prefer a simpler interface over mod managers, the following "trainer" style editors are popular for quality-of-life adjustments: This is the most reliable way to apply