For your second question - whether or not you can use the General's Inspiring Presence to boost the effect of Mindrazor - the answer is simply 'no'.
I Believe this is something that was sorted by an Errata/FAQ of the Main Rulebook so your question is understandible if you only have the actual RuleBook as reference for this question.
- You use the model's unmodified Leadership for Strength-value when Rolling to wound
(this is the mechanic of Mindrazor) which has led to a lot of people arguing that the strength-boost should not even be factored into the negative armour-save modifier of the stricken opponant.
I.e. Mindrazor does not actually increase your Strength (for all purposes) to equal your unmodified Leadership - instead if Mindrazor simply allows you to use your Unmodified Leadership as Strength value specifically when making ToWound rolls in Close combat.
- I don't know what to Think of that last bit to be honest..
As to your first question: I'm simply not sure. So don't take the following as gospel:
I Think if the you look at the Main Rulebook Errata you will find that Impact Hits and Stomp has been bundled together as 'unusual attacks' that doesn't benefit from any Special Rules that the model might have.. So my guess is that the answer to this question is 'no' - Enfeebling Foe and Soulblight does not effect Impact Hits..
Really unsure about that one though..
Someone else can clear this up perhaps?