In most situations Item.ConditionID can be added to or modified for an existing listing by including it in a ReviseItem call, a RelistItem call, or related calls

If the return payload for a GetCategoryFeatures call indicates that Category.ConditionEnabled is set to Required for a category, you can change the ID to more accurately describe the item, but you cannot remove Item.ConditionID from the listing when it is revised/relisted.

Restricted-state listings

If a listing is in a restricted state, the condition is subject to eBay's usual revision restrictions. If you attempt to add or change Item.ConditionID when a listing is in a restricted state, your request may fail.

For example, if an auction has bids or ends within 12 hours, you cannot remove or change its condition. In this case, if there are fields that are still editable on the auction, you will be able to edit them even though Item.ConditionID is not present.

Refer to Item changes allowed during revisions for typical rules about fields that can not be modified when an item is in a restricted state.