Do they have an on/off switch? Use this turn, off next turn...

Nope.

For Enhanced Scopes, no. It's a mandatory effect. If the effect of an upgrade contains the word "may," then it's optional and you can choose whether or not to activate it when it would trigger. Enhanced Scopes simply says, "During the Activation phase, treat your pilot skill value as '0'," (no "may") so it's always "on".

Not unless they say they do, or use the word "May" (allowing you to use it, or not, at your discretion).

Only when optional when there is "may' in on the card.

Therefore, Enhanced Scopes is not optional.

However predator is optional.

Thank you all for helping.