Relaxers and any other chemical hair treatments are definitely "permanent." But locked hair?
Take a look at the above picture. This is one of my microlocks with a lot of loose new growth. Can you tell where the more mature part of the lock starts? Close to my finger right? Well, all of that loose hair above my finger can be easily relaxed, twisted, or interlocked. So ask yourself does that lock that I am holding look permanent? Only you can answer that question from your visual observation.
Also, consider this: If your hairtype is hard to lock, then would not it be easier to "unlock?"
My particular head has two different hair types so the lock pictured above has not wanted to remain twisted so I am going to hand lock it to eliminate the excessive new growth. Interlocking the hair does complicate "unlocking." So if you even think that you only want to experiment with locks for a few months, then I would only coil or twist the hair. I would not interlock nor Sisterlock the hair.
The new growth is still going to grow out regardless of which locking method is used. However, twisting the locks would grant you more length if you do decide to "unlock." Please see my article on this blog about a lock removal tool.
Honestly, I encourage people to try all their natural hairstyling techniques such as twist-outs, braid-outs, etc prior to deciding to lock. Once someone decides to lock their hair, there should be no regrets, only patience.