Hardness and blast resistance multipliers are independant from rock types and would apply to all of them.
For example, a hardness multiplier of 2 would double all rocks types hardness (weak -> 2, medium -> 4, strong -> 6, very strong -> 8).
Blast resistance multiplier of 0.5 would halve all rock types blast resistance (weak -> 0.5, medium -> 1, strong -> 1.5, very strong -> 2).
Idea from SpwnX:
Hardness and blast resistance multipliers are independant from rock types and would apply to all of them.
For example, a hardness multiplier of 2 would double all rocks types hardness (weak -> 2, medium -> 4, strong -> 6, very strong -> 8). Blast resistance multiplier of 0.5 would halve all rock types blast resistance (weak -> 0.5, medium -> 1, strong -> 1.5, very strong -> 2).