Can you use tazorac in the day and renova (tretinoin) at night , given that your skin can handle it ?

Yes: Just make sure you use sunscreen also.

Vitamin A topicals: Tazorac and Renova (tretinoin) are designed to be used at night. They both make the skin sensitive to light/ uv. Both products lose their efficacy when exposed to light/ uv. More is not better. Nightly use for 3/4 months with a 2 month holiday and daily use sunscreen is what i recommend for my patients.

???: Not a great idea. First, sunlight inactivates retinoids so whichever one you use during the don't won't work as well. Second, you really only need to use one retinoid. You won't get any more benefit from using two, or even from using the same one twice daily. Finally, tazorac tends to be harsh and Renova (tretinoin) was made to be very gentle. Strange combination to use both.