Entering data & amending checkboxes

Entering data & amending checkboxes

Please advise:
1. In a checkbox field which can accept more than one value, why does bulk edits destroy any previous data in that field - how can you append data to the field in bulk edits?
2. When adding choices in a checkbox field, why does it destroy all the data in the field? How can I set it up not to if I want to add more choices to the checkboxes in future?

Thanks

Mr. Dahya Mistry
dahya_mistry