mysql re-partition table
What I would do is set it up with sufficient partitions so that your top (MAXVALUE) partition never gets used. In this way when the time comes to add the next partition, you are going to re-partition the 'empty' MAXVALUE partition which should be a lot quicker.

So you would start by adding a partition for VALUES LESS THAN (2300000) which replaces the MAXVALUE partition.

Then when you get close to 2300000 entries, you would add a new partition for VALUES LESS THAN (2350000). And because you would be splitting the empty MAXVALUE partition it will be relatively quick.