Or after, for that matter. Either frozen or fresh.
I rarely buy grocery store pizzas, but when I do I always add more cheese, either parmesan or some grated cheese I have around. I always drizzle olive oil all over and rub some on the crusty edges. Might sprinkle on garlic powder or granulated garlic. Maybe add leftovers like canned chopped tomatoes, green peppers, or salami slices.
Plenty of crushed red peppers after it’s done.
Always. Penzey’s Pasta Sprinkle, Aleppo pepper flakes, olive oil on the crust are the standard additions.
I will usually eat a pepperoni or 2 before cooking it, does that count
Yup. I usually add some mozz, pepperoni, maybe some tomato and feta. Spices, etc.
Yes. My finished pizzas are masterpieces.
I like bell peppers and onions on my pizza. When Papa Murphys has their Cowboy pizza (mostly meats) on sale, I’ll load it up with onions and green bell peppers, and sometimes more cheese.
I’ve also been known to buy their pepperoni pizza when it’s on sale and dump an entire (drained) can of pineapple on top, with extra cheese.
With store-bought frozen pizzas, anything is fair game. Those things are notoriously sparse on toppings.
We have Penzey’s Pasta Sprinkle and ground aleppo pepper. I’ll have to investigate. 
Not always, but usually. We’ll leave half of it bland, for the kiddos. On the other half, we’ll put some combination of:
-Olives (for me only)
-Pickled onions (we make 'em pretty often and usually have a jar of sliced pickled red onions in the fridge)
-Walnuts
-Parmesan
-Dried oregano/thyme
-Feta, if we have it
Of course! I like a few slices of ham on my Tombstone. 
cheese and italian seasoning.
Well…yeah!
Isn’t a law, or a rule or something?
I have jars of Penzey’s Pizza Seasoning and Penzey’s Frozen Pizza seasoning in the spice cabinet but honestly it doesn’t seem to make much difference.
Yeah, with frozen pizza, I don’t want to add any more seasoning to begin with. Most pies are already seasoned much more than I season my own pies. The only exception is that with a frozen mushroom pizza, I may add a little bit of dried thyme to it.
The only thing I adulterate frozen pizza with is pepper flakes or hot sauce these days. I used to add all sorts of additions, but it still tasted like frozen pizza to me, so why bother wasting my good ingredients and time on that? Don’t get me wrong – I try to always have at least one frozen pizza in the freezer, but it’s just pepper flakes or hot sauce that goes on it.
I don’t eat frozen pizza, but when I bring home a fresh pie from the best local pizzeria I generally sprinkle a little dried oregano, granulated garlic, and crushed red pepper on every slice. Not that I don’t trust them to make good pizza, but I enjoy the augmentation.
More cheese, more sausage. The wife loads her side up with all kinds of vegetables. By the time we’re done I’d swear it weighs four pounds.
My goodness. Why not just make a casserole?
I do it differently. I get either a plain cheese or a vegetable pizza. I knock off most of the cheese, because gobs of greasy mozzarella don’t do anything for me. I add more veggies, garlic, sundried tomatoes, and then dab on blue cheese or chevre.
If the crust is good, (rarely, but sometimes it is), I dip the ‘pizza bones’ in blue cheese salad dressing.
Well, that’s why you’re Superma–uh, oh!
Always onion powder, black pepper and red pepper flakes before cooking. And if I have it, a little mozzarella goes a long way on a frozen pizza.
Usually just buy the frozen crust - gluten free - and top it. I will add more pepperoni to a pizza.