ever had a parts

ever tried to improve the internals of a device and have it backfire? For example, the caps in my tube phono pre were professionally upgraded, and yes, it is clear and fast and dynamic - but now I just about jump out of the chair on a skip or scratch, and sibilance on some vocals seems to have increased. Now I am thinking twice about "upgrading" caps in the power amp. There seem to be two schools of thought, and one camp seems to think better parts are almost always a good idea, and another, that the "voicing" the designer achieved will be disrupted by any change, not necessarily for the better.