Just some minor instructions:

The file downloaded in not completely ready since it will contain all 5 creepers at once. They will be named: Beachcreeper(.png) (sand), magmacreeper(stone/magma), shroomcreeper, icycreeper and cactuscreeper. This pack is not a mod so you may only use one texture to replace all creepers. To do so rename the desired "creeper" to specifically "creeper.png" then zip up the all files again and drop it into the resource pack folder.

Edit Again: With help from the various communities I haunt (youtube/reddit) I was able to learn how to make this into an actual optifine mod, the creepers will actually changed based on biome! Sadly Optifine is still out of date on version 1.14 so you will have to play on an older version. So I'm modifying this post to include not just the texture pack but the optifine creepers as well. There was an error in the mod it should be fixed now.

I fixed the download, each creeper now has its own zip file you can drop directly into the resource packs folder, keep in ind there still can only be one active at a time thought (guess I should learn mods too lol). I also added a two new ones:

Birch and Swamp: