Below are the changes that need to be done for ACS in OpsMgr 2007 to work on a port other then the default of 51909. I tried it in my lab here and it worked but the usual caveats apply. 

1. On the ACS Collector server make the following registry change, adding the custom port you want to use:

a. Stop Operations Manager Audit Collection Service.

b. Go to HKLM\System\CurrentControlSet\Services\AdtServer\Parameters and change the value for Reg Key named AdtAgentPort. (Default value will be 51909)

c. Start Operations Manager Audit Collection Service.

d. For verification you can run netstat –a command from command prompt which will show that now the server is listening on your newly configured port.

2. On the DNS Server for the domain where the Collector server and the Forwarder machine belongs, you need to create a new SRV record:

a. Open DNS Management, Server – Forward Lookup Zones – Expand your domain name – Right click on _tcp and click ‘Other New Records…’

b. Select Service Location (SRV) under Select a resource record type and click Create Record.

c. Configure Service as _adtserver, Protocol as _tcp, Priority as 0, Weight as 100 and Port number as value you have configured on collector server in step 1.

d. For the Host offering this service, type the FQDN of the collector server.

3. On the ACS Forwarder machine, make the following registry change:

a. Stop the Operations Manager Audit Forwarding Service.

b. HKLM\Software\Policies\Microsoft\AdtAgent\Parameters and change the value for Reg key named LocalConfig from 0x00000001(1) to 0x00000000(0).

c. Start the Operations Manager Audit Forwarding Service.

Once this is complete, the ACD Forwarder machine will locate the SRV record from the DNS server and connect to the ACS Collector server on the newly configured port.  You can verify this using netstat command from a command prompt on the Forwarder machine.  Also you can check for Event ID 4368 in the Application Event log of the ACS Forwarder machine which should say something like “Forwarder successfully connected to the following collector: FQDN:Port."

Note: This information was originally contributed by Milan Jajal on the Operations Manager Support Team blog: