Hello, sorry to bother you, how to modify the melting point of RBMK fuel rods?

Fuel stats are defined here: https://github.com/HbmMods/Hbm-s-Nuclear-Tech-GIT/blob/master/src/main/java/com/hbm/items/ModItems.java#L3573

If you just want to disable meltdowns without compiling the mod yourself, change the gamerule dialDisableMeltdowns to false.