If a Blade Adept arcanist takes one of the available magus arcana as an exploit, can s/he then take the Extra Arcana feat to gain other magus arcana?
Can s/he select arcana that are not arcane accuracy, close range, critical strike, dispelling strike, or hasted assault?
First of all, he can take Extra Exploits to gain more arcana from his list.
I believe, by the precedent of Oracles with Channel Energy feats, that he should be able to take Extra Arcana. However, his ability is not "Magus Arcana Class Feature (or equivalent)", it's "Magus Arcana Class Feature (or equivalent), (limited to this set of arcana)" and that limitation carries through to anything using the ability as a prerequisite.