it is not recommended and may cause damage to your instrument.
The tension of the extra string can warp the neck and cause the intonation to be off, compromising the playability and sound of the bass. Additionally, the extra string may interfere with the tuning of the other strings.
A 5 string bass is designed for its specific string configuration, and altering it can
negatively affect the performance and lifespan of the instrument.
If you're seeking a heavier sound without tuning down, consider using thicker strings, experimenting with different string materials or playing techniques, or using external effects like distortion or compression to achieve the desired tone.