can you reverse feedback

[mippsaublue]

Is it possible to reverse feedback given?

[digital*ghost]

If it's a positive, no, sorry. Feedback can only be revised when it's a neutral or negative. 

[amber-eyed-girl]

yes, in certain circumstances it can be removed, revised or a follow up comment can be left.

See http://pages.ebay.com.au/help/feedback/questions/remove.html for what is applicable for you.

If as Digi says, it's a positive, a follow up comment can be made to the original feedback.

Also, if a seller leaves a negative remark with their positive star, you can apply to eBay to have it removed.

http://pages.ebay.com.au/help/policies/feedback-removal.html talks about what can be removed.