Make Pepperoni out of Regular Salami

Pepperoni is basically just a spiced pork and beef salami with some smokiness in it, you could achieve a similar flavor by using some smoked chili powder like paprika or chipotle. You also aren't going to get very far trying to make a salami spicy by adding pepper to it beforehand, like injecting it with some sort of spice mix as there's not enough moisture to allow the spice to mix in. You'll have to add spice to the sliced salami, the question is how to apply that seasoning so the flavor seems to come from the salami when eating the pizza. Chili powders will burn in the high temperatures of a pizza oven, producing off flavors and an unappealing look, so sprinkling them on top of the salami slices is not the best idea.

You have 2 good options:

1. Add the spice to the pizza sauce: this will make the whole pie taste of the spice and may not be what you want. It's the quickest and easiest solution though
2. Rub one side of each sliced salami piece with the spices, and then put them on the pizza spice side down. This will localize the spice around the salami slices, and put the salami between the spice powder and the heat source so it doesn't burn. This is a bit of extra work but I can't imagine it being that big a pain

Personally I'd go with option 2 as you'll get a nice hum of spice around the salami and some on it when you bite. It won't be quite a pepperoni but I bet it will be very close.

You can marinade salami in the pickling liquid of canned pepperoncini around 10 minutes for that slightly off-sour taste and bite. Just drain it thoroughly and pat it dry before using. The acid helps permeate the fat content of the salami.

As GdD suggests, you could add a teaspoon of smoked paprika and chipotle powder to the mix to give it that depth, and a bit more kick.

Trader Joe’s Bomba sauce (roasted Calabrian peppers), olive oil, smoked paprika...let it marinate with salami for a few hours=best pepperoni/chorizo ever!!!

This might be really difficult to get hold of where you are, but I can fool people into believing there's hot, spicy chorizo in a dish by using Canarian red Mojo powder. Add that to a salami & I'm sure few could tell the difference - so long as it's a Southern-European-style salami, not like a traditional Danish, for instance.

It's a dried blend of red chilli, garlic & cumin. It is traditionally made up into a sauce with oil & vinegar, but that's not necessary for this.
Though the ingredients would seem very simple, it does have quite a specific flavour profile, that just those few ingredients would not hint at in themselves. Because of this, I'm uncertain if making your own would come anywhere close compared to the real thing.

You may be able to get the Cuban variant, but I have never tasted that so cannot comment on its similarity or otherwise.