Is it safe to change the type of filler for the same area after 6 months?

Yes, you can change fillers. I can't speak to Revanesse Ultra because it's not FDA approved. However, for nasolabial folds, I recommend a combination approach with fillers for the folds themselves and to provide anatomical support, Sculptra for collagen building, peels and lasers for texture and tone, with radiofrequency/ultherapy for skin tightening. I recommend getting a formal evaluation with a cosmetic dermatologist. Best, Dr. Emer

Thank you for sharing your question.  If you have reached a cheek size that you are happy with you can certainly move forward with additional placement of a thinner filler like JVD into the nasolabial folds to smooth the transition from your cheek to your lip.  Due to US restrictions I have never used Revanesse Ultra.  Hope this helps.