A new director in an existing Brocade fabric and "Port Based Routing Policy"

In an existing SAN with multiple Brocade fabrics we are in the process
of deploying two new 4/256 directors. The existing fabrics are all 1 or
2Gbp switches with a mix of 2800, 2400 and 3900 models. No other 4Gb
switches are present.

As I understand it, the default routing policy for a 4/256 director is
Exchange Based Routing
Policy. This is however apparently a problem with the storage system
used (HP EVA) and we must change to Port Based Routing Policy.
This is all well and good, but from a solution text I've recieved, the
procedure calls for all switches in the fabric where the 4/256 director
is deployed to be disabled via "switchdisable", the routing policy
changed on the director and then all switches are re-enabled.

Apart from the new directors, the existing fabrics are in a production
environment and we would very much like to confirm if it's truly a
requirment to disable the existing switches. We're not making any
configuration changes on them, and as far as I can tell Port Based
Routing Policy is the only routing policy available on them.
Would it possible to disconnect the directors from the fabric, make the
routing policy change, and reconnect them?

This is fairly urgent, and I would appreciate any comments.