Do I need to modify the Microsoft iSCSI configuration after I modify the storage network?

What do you mean with "Storage network"?

Are you running out of network ports on a switch, and are you just adding 2 more switches (each switch linked to 1 of the pre-existing switches) to get more ports?

Something like:
Fabric A:
Switch 1 and Switch 3 (linked together):
Server1 PCI1, Server2 PCI1 and AIX150i-SPA0 connect to the Storage Network A; AIX150i-SPB1 connect to the Storage Network C.

Fabric B:
Switch 2 and Switch 4 (linked together):
Server1 PCI2, Server2 PCI2 and AIX150i-SPB0 connect to the Storage Network B; AIX150i-SPA1 connect to the Storage Network D.

In an EMC SAN (Storage Area Network) the following terminology is common:
- Host = a computer running a server operating system that is/will be using storage space on 1 or more storage systems
- storage system = a system that has 1 or more harddrives and will be providing disk space to 1 or more servers (e.g. AX150i)
- fabric = a fibre channel or ethernet network (can be 1 or more switches) that interconnects hosts and storage systems (and possibly tape libraries (more common in fibre channel, but iSCSI tape is starting to show up ( example)

A typical SAN would have 2 or more hosts (if you only have 1 host, you may as well go direct-attached) using 2 fabrics (for redundancy) and 1 storage system.

Thank you for your reply.

I don't add 2 more switches to get more ports. I have created two VLAN (Storage Network A and Storage Network B) at two switches for storage data communication between database servers and disk array. The disk array has dual SP (SPA and SPB). (SPA1 and SPB1 connect to network A, SPA0 and SPB0 connect to network B).

Now I add another cluster, and I use the current two switches for data communication between database servers and the current disk array. I plan to add two new VLAN (Storage Network C and Storage Network D) for the new cluster (SPA1 connects to network A, SPA0 connects to network C, SPB1 connects to network B and SPB0 connects to network D).

The current two database servers use SPA0, SPA1,SPB0 and SPB1 as the targets in the Microsoft iSCSI Initiator. I don't want the SPA0 and SPB0 are used by the current database servers, so I need to remove these two ports from iSCSI Initiator manually? 

What you have described is doable, and you are correct, you would have to manually log off the SP ports from the MS initiator.  However, if I were setting up what you have described, I would leave the SP iSCSI ports the way you have them and just add the cluster iSCSI NICs to the existing VLANs.  I would also have all hosts connect to all 4 SP ports.  However, if you want to test performance differences you can simply disconnect 2 of the sessions in the MS initiator.   No matter how it is VLANed, all 4 ports will be listed in the targets tab, you will choose which ports to log into.