@
andysoup - Yes - it is old, 3 years old in fact
Meantime calibre has acquired a feature rich ePUB Editor. The calibre Book Editor provides a simpler and
safer means of editing an ePUB — such as built in integrity checks et-al — than unzipping it and fiddling with a context-unaware text editor on individual components. The Book Editor can be used from within the Library Manager or independently.
And if for some obscure reason the Calibre Book Editor doesn't suit,
Sigil is a just-as-good-as alternative, and it was first released in 2009! Latest release was Dec 2015.
BR