The options below are initial suggestions. A lot is dependent on your setup. All the docs are on 12.5 SU1 but if you're on an earlier version just look for the docs w/ the same name. I'm assuming UCCX DAL server is live so it can be added to but not completely overwritten.
(a) The easiest and safest way is move scripts, prompts, agents etc in batches according to the Contact Center they are in from SJC --> DAL. In other words, when you re-register the SJC phones to DAL plan to move related UCCX config over as well Contact Center by Contact Center. Benefit to this is you can roll back pretty easy, just re-register phones back to SJC, move carrier forwards back, keep SJC UCCX server up and things will be fine. Downside of this is that some old historical data would be on the SJC UCCX server. Also, you'll need to make sure you had enough licenses and CTI ports on DAL server to handle the additional usage as well as making sure server is sized properly in terms of virtual resources for additional load.
Contact Center Express Virtualization Guide:
https://www.cisco.com/c/dam/en/us/td/docs/voice_ip_comm/uc_system/virtualization/virtualization-cisco-unified-contact-center-express.html
(b) Other way which would need a bit of investigation is to integrate SJC UCCX server with DAL UCM. It is possible, according to design guide, to have 2 UCCX servers linked to one UCM cluster as long as UCM cluster is sized for it.
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/crs/express_12_5/design/guide/uccx_b_solution-design-guide-125/uccx_b_solution-design-guide-125_chapter_010.html
---> Multiple Cisco Unified CCX Clusters Integrated with a Single Cisco Unified Communications Manager Cluster
You could you could use back up/restore from SJC UCCX server to new DAL UCCX server in isolated subnet with same hostname/ip and then change hostname ip (I'm presuming you would need the server w/ hostname/ip on the DAL network) and then integrate with DAL UCM. You don't have to move SJC agents until DAL UCCX server works with DAL UCM.
Back/Up Restore Considerations: https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/crs/express_12_5_1_su1/maintain_and_operate/guide/uccx_b_1251su1admin-and-operations-guide/uccx_b_12_5_2admin-and-operations-guide_chapter_011011.html
Hostname/IP Change:
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/crs/express_12_5_1_su1/maintain_and_operate/guide/uccx_b_1251su1admin-and-operations-guide/uccx_b_12_5_2admin-and-operations-guide_chapter_01011.html#topic_4DA1FDC6CCC362...
Option (a) is the easiest but takes longer. Option (b) would need tested out, in a lab environment, to see what else would come up beyond what's in the documentation.
Wish you all the best.
