Not sure it qualifies as fully "automatic", but there's an Exclude button at Common Service - Device and Credentials - Device Management

"You can also remove the list of devices that are excluded earlier using the Exclude operation." -- according to the contexual Help.

It sounds like it could be a one-time manual effort to carefully craft an Exclude list based your old IP ranges (making sure it's mutually exclusive to your new ranges), click the Exclude button once to upload the list, then click Exclude again to actually get rid of the old-IP devices, after which the exclusion should become "automatic" based on the Exclude list. At least that's how it reads to me at first glance:

Excluding Devices

This feature allows you to specify a file that contains the list of devices that should not be added to DCR using Add or Import operations.

During the Add or Import operations, DCR ensures that the device being added or imported is not listed in the Exclude Device List.

You can also remove the list of devices that are excluded earlier using the Exclude operation.

The file containing the list of excluded devices should be in CSV format. See A Sample CSV Exclude File for a sample CSV file used for Exclude operation.

You can exclude devices by specifying any one or more of the following fields in the CSV file:

management_ip_address
host_name and domain_name
device_identity

If you are using a CSV file generated by the DCR Export utility to exclude devices from Add or Import operations, make sure to remove the sections related to AUS Managed, Cluster Managed and CNS Managed devices from the CSV file.

To exclude devices from Add or Import operations:

Go to the CiscoWorks home page and select Common Services > Device and Credentials > Device Management.

The Device Management page appears.

Alternatively, you can navigate to this page from the LMS Portal home page if you have installed the LMS Portal application on CiscoWorks Server.

Click Exclude.

The Upload Exclude Devices File dialog box appears.

Enter the file name or click Browse to browse the file system and select the file.

The file that needs to be uploaded must be in CSV format.

Click Apply to upload the file.

The system displays a message that the devices are excluded successfully.

A Sample CSV Exclude File

; This file is generated by DCR Export utility 
Cisco Systems NM Data import, Source=DCR Export; Type=DCRCSV; Version=3.0  
; 
;Start of section 0 - Basic Credentials 
; 
;HEADER: management_ip_address,host_name,domain_name,device_identity 
; 
,Dev1Hostname,, 
10.1.0.60,,, 
,,,AUSID1 
,Dev2Hostname,cisco.com, 
; 
 
;End of CSV file 

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