I am trying to increase the range of spawners. 

 - RequiredPlayerRange
 - SpawnRange

are both values inside every spawner block, and I want all spawners in the overworld to have new values. 

How would I go about achieving this? Thanks. 

As D7 said, it's not easy, but it is possible
basically you need to create a custom SpawnerBlock, SpawnerBlockEntity and MonsterRoomFeature (you can extends the vanilla classes)
inside the SpawnerBlock you need to overwrite the methods SpawnerBlock#getTicker and SpawnerBlock#newBlockEntity do the same logic than vanilla but with your BlockEntity
inside the SpawnerBlockEntity you need to set the BaseSpawner of the SpawnerBlockEntity to a custom one (needs an AT)
inside the MonsterRoomFeature you need to run the vanilla logic but you need to place your custom BlockEntity

then subscribe to the BiomeLoadingEvent remove the vanilla MonsterRoomFeature and add your custom MonsterRoomFeature

another way would be to make a PR, to add for Example an Event for that (BlockEntityPlaceEvent) -> Note: this is in my opinion the better solution but it will take some time (min 1 Month)

Edit: the BlockEntityEvents are actually a good idea, when i have time i will make a PR for that

Edited November 20, 20213 yr by Luis_ST

@Luis_STif you can make something where you can edit the nbt data of any block from a config file, and have it automatically replace any instances, that would be a legendary feat that I'm sure would be heavily utilized by modpack creators (myself included)

This idea has tremendous value. I can think of many ways this could be utilized.