you cannot start at the higher number because the BCM goes ahead and assigns the numbering plan using your start DN and then counting up by one until it assigns to all POSSIBLE B1 DN's B2 DN's VOIP DN's Hunt Group DN's etc...
This encompasses 594 DN's on your system. If you started any higher, then the DN's would roll up to a higher number of digits..
to wit 9600 + 594 = 10194 - As you can see, this makes the DN length now 5 digits.
So unfortunately, there is no way around this but to do a renumber, like everyone has suggested.