There was some discussion here recently about eluting primary antibodies off of tissue by using an acid, something below pH 2.5-3. If you could get the primary off, the wrong secondary may come off with it, and then you could start over from the beginning.  Otherwise, if your primary was used at a concentration which was determined to be optimal for getting good signal, I don't think putting more primary on would result in any additional staining.  I would be interested in hearing again about the acid elution of primary antibodies anyway, specifically, if the primary comes off, DOES the secondary, ABC and DAB also come off, or just the secondary and ABC, leaving the precipitated DAB in place?
Joyce Kotzuk
Univ. of New Mexico neuropathology lab