3. Conversion of NEMstake tokens to NEM: Owners of NEMstake tokens need to send the total amount of tokens he owns back to the issuer with a message (use the message function within Nxt asset exchange) in the form: (Quantity of the tokens) space (NEM receiving address) in order to receive the corresponding amount of NEM in the receiving address.
This can be simplified even more. Our Asset Transfer transaction also has a "comment" field where you can put arbitrary text (1000 chars limit). So the token owners can put only their NEM address in the asset transfer comment, no need for separate message. Then, after you (the issuer) send them the actual NEM, you can destroy the token by transferring it to the Genesis account, and in the comment of that asset transfer put the NEM transaction id, as a record that the NEM has been issued and sent.