Modifying the CoreRPG ruleset

[Trenloe]

Would I be correct to assume that effects like those seen in 2E and 5E are part of the specific ruleset and not part of CoreRPG out of the box?

Correct. As @damned mentions - the base effect coding (CT, durations, etc.) is in CoreRPG. However, rulesets have their own effect manager for things specific to that ruleset (e.g. RESIST coding, damage types, etc.) - usually in scripts\manager_effect_<ruleset>.lua. Then, each action manager (the code that runs when an action is made - damage, attack, saving throw, initiative, etc.) has code within that checks for active effects that are relevant to that action and applies the relevant adjustment/modifier. So, look in the 2E or 5E scripts\manager_action_XXX.lua files

[esmdev]

Great, thanks.