Hi, I usually treat cell with antibody, and I dilute the antibody into the medium, it always works fine. If you like you can try, it should be fine. Good luck!
I would not generally advise this as cells will stick to cell culture plates generally, so you would waste time and antibody. If you want to perform an enrichment/purification step then you can use an antibody magnetic separation step to purify cells which express you protein of interest, provided it is expressed on the cell surface of course. follow this link