Right now, bamboo spikes can be tipped with any potion effect, with a config to only allow harmful or neutral potion effects.
Relevant code.
My suggestion is to have a more granular configurability with the ability to blacklist individual potion effects, rather than just 'all beneficial on/off', with no way to disable neutral/harmful potions.

Ideally, this would be defined by some sort of tag rather than a config, so that other mods can disable their potion effects from being added to a spike.

The particular reason I'd like this feature is that I'm a mod dev, and the ability to apply potion effects from my mod to spikes has broken the intended progression somewhat by allowing some exploity-combos.

I'll make it a tag like I did with skeletons tipped quiver arrows