I'm sorry there is just no way that this upgrade is togglable. The card itself tells you it is always on. Otherwise it would say ""You MAY treat the attack as obstructed". Other "While" effects will have the term "may", but this one doesn't give you an option. It's always on "While" squadrons are shooting at each other.
There is literally no wiggle room on this... it is crystal clear.
100% true.
HOWEVER, the RRG specifically states that all upgrade cards are optional to resolve, UNLESS SPECIFIED OTHERWISE.
And JF doesn't specify otherwise. No cannot, for example.
The likely intent is that it's always on (IMO), but it does a poor job of conveying this.