Since 'S ick' and 'S i c k' are both valid gamertags, there's no way that you can change 'S ick' to 'Sick' once it resets, because the system will look and see that 'S i c k' is valid, and it will not let you change it to 'Sick.'
This is considering that 'S i c k' will not be reset. While it may be reset, there's no guarantee that 'Sick' will reset as well, in which case you will be stuck with 'S ick.'