Hi Zymos,
thanks for your question!
Once you stick on the Overlay it can be pulled off again but it will most likely be damaged/destroyed in the process. So I would consider it permanent.
You could try to cut out the carrier foil on which the sticker sits to match the sticker. This way you can lay it on and off. I must say I don´t have experience with this though and I don´t know how well the carrier foil will hold over time.
You could also still stick it on the BCR, and then lay on other overlays you create on top. Depending on the top overlay, the buttons should still stick out enough so it´s still fun to use. I tried it with a custom paper overlay on top and for me it would be satisfactory. Of course you´d have to see if that´s the right way for you too.
Cheers!