Modifiers to die rolls

[Tittliewinks22]

I could not find the answer to these questions, so I'm asking here.

Does the modifiers for a die roll effect special abilities?

Examples:

Spirit Hosts or bloodletters are at a -1 to hit.  If you roll a 6 on the die, is it treated as a 5 for the purposes of their mortal wound on a 6+ rule?

I was under the impression that this is the case, but does that also mean the Runefather's Weapon Breaker attack only works vs a weapon with no rend value?

Thank you.

[BaldoBeardo]

Short answer is yes. Modifiers affect 'trigger' numbers - with the exception of abilities that trigger rerolls, as rerolls must occur before modifiers.

In the case of the Runefather's weapon breaker, don't forget you can also get +ve modifiers to your save rolls...