Can the collar be removed from the main part after sliding in and locked?

The slide-lock structure is designed to make sure it won't fall from the animal after deployment.

If the device has already been deployed to an animal and needs to be removed for some reason, you can cut the collar part to avoid hurting the animal.

If the collar and the main part are connected and locked by accident, you can remove the collar from the main part with a hammer as shown below.

Note that, after being disassembled, the connecting part between collar and main part could be worn down and collateral damage may happen to the main part. So it is not suggested to deploy the device on another animal. However, if you have to, please test the device properly to make sure the device works fine (e.g. air tightness), and apply glue to the connecting part to secure it.