Regarding mutations and maximum characteristics

Do the mutations (and other misc bonii) in their many sources count towards a units maximum characteristics.

Ie, can an extra arm take a human to 5 attacks?
Can the leaders blessing of nurgle from the marauders warband (BTB) take his toughness potentially to 6?

and if possible could you point out any sentence I forgot to read in the rule book regarding this > . <

Cheers for the help guys

Mutations are like skills that add to the profile. So if you e.g. suffer -1 Movement, then this is always added to your normal Movement. So your profile reads 4 and you subtract -1.

This is also the case with Serious Injuries. If you suffer -1 Toughness permanently, then this does not affect your profile - it is added on top. So you cannot make up for these modifiers by stat increases through experience.