When shot into claims by mods such as FTBchunks or OPaC, blocks can be placed and broken (Albeit slowly) regardless of claim settings.

Most non trivial modded interaction will break claims. The game does not have a claim syatem. All claims mods are brittle and there will be exploits with mods. Maybe very very rare and hard to find but the core is a mod can set a block at an arbitrary position and there's no programmatic way of knowing if that's due to an action caused by the environment (imagine a volcano mod shooting meteors at random) or something I directly caused by the player (imagine the player pressing a button to fire the same projectile from dispenser)