Many times, one set of dial-in (level, filter and  time dial selection) may work on certain passage, and then later down the wave form, you need to re-dial to fine tune others, but in doing so, it may changed earlier results.
 
A locking feature ensures that you can fine tune and select required hits as you move along.

Nice...    Locking transient markers sounds like a good idea as a general AudioSnap feature (assuming it doesn't already exist) that would be very useful in Drum Replacer.