Gravestones are spawned along with treasure chests - they're just top-side markers (you can't decrease just gravestones). So if there's too many chests, you increase the numbers in the lines:
which increases the number of chunks (16x16 blocks) between chest spawns.
You can also decrease these values:
which will reduce the probabilty that a chest will be spawned when the chunk counter (from above) has been hit.
So a combination of both can really reduce the spawn rate.
In the reply above I explained how to decrease the frequency of the chests spawning. Just do the opposite. ie. decrease the values of the I:chunksPer[Name]Chest and increase the values of the I:[Name]ChestGenProbability
A backup is always a good idea It *should* be compatible with the older version. However, if you changed the config file any, you might have to update it after you install the new version because I re-arranged some of those values.