I keg my beer and use force-carbonation to carbonate it. Does anyone know if there are any negative consequences to over-carbonating the beer, other than excessive foaming? Are there any long-term affects on the taste, texture, aroma, etc. if one were to over-carb a beer and then allow it to come down to normal carbonation over time?
The release of CO2 can take certain volatile aroma compounds with it. Sometimes this is a good thing (it can strip sulfur notes out of beers) but can also take hop aroma compounds, less than ideal if it's dry-hopped or heavy on late-addition hops. In this case you might notice a slight loss of hop aroma.
Any foaming caused by degassing will also affect the foam of your finished beer, too, since the foam-positive substances (mostly proteins and bitterness compounds) which create foam during degassing won't redissolve and therefore won't be there to help create foam later on. This isn't directly related to over-carbonation, but is still a concern.
Try to degas as gently as possible, and try not to overshoot. As you say, do it over time. Other than that, there's not much detriment to it.
Carbonation can be used in the same way as temperature is used to mask flavours. Just as the colder a beer is the less flavour is noticeable, the more carbonation the less mouth feel, texture, and flavour you will detect. To test this out, try a can of warm flat Coke. Very sweet, much smoother.
Franklin has already answered the degassing part. Also I'm not sure how your beer would come down to a normal level of carbonation over time unless you have some kind of a leak.