The add-on adds the following to the bottom of the front/back templates:
<!--
ANKIHUB_END
Text below this comment will not be modified by AnkiHub or AnKing add-ons.
Do not edit or remove this comment if you want to protect the content below.
-->
So it’s recommended to put your modifications below this comment at the bottom to make sure they are preserved.
Your field will get removed. Adding/deleting fields is not currently supported and might cause problems in some cases (e.g. if you suggest a new note with the updated fields and it’s accepted into the deck you might get errors on the next sync - see Why did i get this error?).