It's not the 'relacquer' per se that does the damage - it's the buffing/polishing. The hip thing to do now is to chemically strip the old lacquer and dip it for tarnish removal, wash, dry, and clear coat. This way the horn still has the old look but you can live with it. Another way is to lightly bead-blast to give it the matte look, then lacquer or plate. The blasting does not remove metal and hides pitting or other irregularities that would have been buffed out with a conventional relacquer. The final way is good but also controversial - hand polish, then lacquer. This could be done a hundred times without any noticable loss of detail, but the surface won't look 'new'. The key to it is to remove all residue of the polish and oxidation before coating, or it won't last long. If you ever have the springs removed for any reason this is a good time to at least go over the horn, clean it up and get rid of any corrosion/discoloration. You can do it with the springs in but you will get painfully stuck many time by the needle springs. Of course, you could just strip the lacquer and figure on dipping it every year to clean and remove tarnish. This could basically be done for many, many years without removing enough brass to make any difference.