Your vehicle should have Switchable Locking Retractors -- pull the shoulder belt all the way out very slowly & it should make a clicking sound as it retracts to indicate that it is locking.... This means that it locks up at the retractor, not at the buckle, so the belt will remain locked if the buckle is at the edge of the carseat shell/frame (this is only a concern with locking lap belts). Check out >
CPSafety - Your online child passenger safety resource for info on different types of seatbelt locking mechanisms.
If you're trying to install in the center with a lap belt, you can merely twist the buckle stalk
up to three full 380 degree turns to shorten it. If the lap belt straps are still perpendicular to the buckle plate then you can twist the long strap at the seat bight/crack so that it lies upside down & will remain in the locked position. Keep in mind, however, that a correct/secure (less than 1" movement
at the belt path) installation outboard is safer than an incorrect/insecure center install.
You would have to contact Toyota directly about new buckles or
LATCH, but I believe it's not possible & if it is it's probably very expensive!