Revise a listing

[2013sebolt]

I have an item that had a bid, received a message from a member wanting to buy for $xxx (the price I'd like to get out of it); my response (because I saw there was a bidder, and didn't know the policy and want to be fair) was to place a bid as I did not have a "buy it now" price... My question is can I revise the listing to have a 'buy it now' price?  I don't want to tick off the bidders (one is who asked about buying at the 'x' price by message), and i don't want to get greedy and lose out on selling it. I also do not want to get into a policy issue with eBay for doing something I should not have done.  I rarely sell things on here and when i do am thrilled to get what i get out of them...selling it for my daughter and her father wants more out of it than what the bid is at...

Suggestions are appreciated.

Thanks!