I know Focus tokens can be spent on a turn even when no Focus results appear on the dice. My question is: can one spend a Focus and choose not to modify Focus results. For example RAC is attacking and rolls only a single [hit] on 3 dice. I roll, blank, blank and Focus and his Hot Shot Co-Pilot requires me to spend my Focus. Can I spend and modify nothing and take the single hit rather than face the wrath of his Gunner?

When you spend a focus for its normal purpose (including being forced into it), you have to change all focus results, even if you don't want to (hotshot co-pilot was made for that purpose)

If you look at the FAQ, it mentions for TargetLocks you can spend it and choose not to reroll anything.

However, when it talks about Focus tokens it does not say anything along the lines of "may"

Unless you have something else to burn the focus on and you really dont want to mod those eyeballs, you cant spend the focus at all unless you wanna mod those eyeballs.

If you spend the Focus for the normal purpose you change ALL "eye" results.

With TL you get to choose how many and which dice to reroll so selecting zero is valid. When you spend a Focus to change results you change the results as they currently are. Now if you spent the Focus, changed the results, and then rerolled some dice and got new Focus results those new results wouldn't change but that's because you've already spent the Focus; the once per modification period rule also keeps you from spending a second for the normal purpose of changing the results.