Block attempt as unlocked, then locking before blocking

Heys!

I'd like to know what happens if one of my minions has Starshell Grenade Launcher, this minion is unlocked and attempting to block. Is it possible at any given window to lock this minion to give -1 stealth to the action vampire AND still being able to block the action?

Name: Starshell Grenade Launcher
[FN:C, Third:PB]
Cardtype: Equipment
Cost: 2 pool
Weapon.
1R aggravated damage each strike, only usable once per combat, and only usable at long range. The minion with this equipment may lock to give an acting minion -1 stealth for the current action.
Artist: William O'Connor

You can trigger the -1 intercept anytime during the block attempt when you have the impulse but the locking of your minion makes them an ineligible blocker from then on if no unlock or wake effect is played after it. [LSJ 20010702]