Question about caffeine-free brewing

Hello! I’ve been doing continuous brewing for about a year now. Using a mix of green and black tea. I talked to a friend recently who loves booch and used to drink it but now has a pretty severe caffeine sensitivity. He can’t even drink white tea. I was thinking of trying to brew using rooibos. Is this ill-advised? Will this transition kill my scoby? Also how would I do it? I normally keep 2-3 inches of the liquid in my carafe with the scoby before adding new tea and sugar. I don’t know how many generations like that it would take before it’s 100% caffeine free. What can I use as the scoby liquid to start a new brew if I can’t use the old, caffeinated kombucha?

Thanks for any tips or suggestions!