Trapped locker is a barrier with dex/disable 9 or strength/melee 11.
Mattock : reveal to add a d8 to your noncombat strength check. Recharge to use strength or melee in place of the normal skill in a check to defeat barrier with the lock or obstacle trait.
Could you in this case reveal the mattock (to add a d8) then recharge the mattock to change the dex/disable check into a strength check at the lower pass of 9 ?
No. You can reveal OR recharge since it doesn't say "additionally" or "you may also".