There is no alternate starter. You use the starter for what you want to brew.
If you want to make kombucha, you have to use kombucha starter.
If you put milk kefir grains in a jar with tea, you're not going to get kombucha.
The starter you use contains the microbes necessary for what you're making.
Vodka in sweet tea, with some ice, will make you a hard iced tea, not kombucha.
If you use kombucha starter, with new sweet tea, and add vodka, you'll get very strong vinegar very quickly. I've got a post somewhere where I did this on purpose. 50ml of vodka in 3L of kombucha will get you very high levels (relative) of acetic acid in about 5 days. Unless you enjoy a glass of very cloying vinegar, I don't advise this route.
Distilled white vinegar will not do anything on it's own other than add acetic acid and lower the pH.
If you are wanting to experiment with adjunct flavors, keep your primary fermentors making plain "base" KT. Then rack to a secondary fermentor and flavor with adjuncts there.
To flavor with different types of tea, you can do that as well. Just keep your primaries making plain KT, and use that finished KT as the starter for separate containers to which you add your different tea solution. Just keep in mind that the first batch would be diluted, as it is (1) part plain "base" and (2) parts flavored/different tea.
An example setup:
Fermentor-A contains your "base" KT. Fermentor-B and -C are experimental. All containers are 3.785L(1 gallon), with a 3L fill line.
Ferment "A" to where you like it, then transfer 1L to "B" and 1L to "C".
Make new base tea, and refill "A".
Then make test tea solution α, fill "B" to fill line.
Then make test tea solution β, fill "C" to fill line.
Make sure all jars are clearly marked (sharpie or paint pens work fine on glass), note the solutions, and which container they went to in your notebook. If you process all jars on the same day, you can let all 3 ferment the same amount of time, then take samples and record the tastings in your notebook. Fermentor-A will be your control.
You'll want to note things like the level of tea flavor, decrease in sweetness, increase in sourness, and pellicle growth.
