Hicks: He will be armed against fortune
Yonge: he will resist fortune,
Mensch's seems to translate this as: "he will face his destiny" which seems more Stoic than Epicurean.
Original text: τύχῃ τ᾽ ἀντιτάξεσθαι,
There no negation in the original (other than the prefix ἀ), so this characteristic is fully governed by the verb.
ἀντιτάξεσθαι = will be set opposite to (necessity), will range in battle against (fate)
τύχῃ (dative case) = (by/for) necessity, (by) fate
Suggested option for translation: He will oppose fate.