LTM replacement question(LTM as a server of the other F5 DNS): Is there any problem of the crt?

I want to replace a pair of LTMs(1600 to i2600, v11 to v13), but the LTMs are the server of another F5 DNS. Is there any problem should I concern?

I configuated the new LTMs with the ucs files of the old LTMs, but I generated new device crt when I configures HA group at the same time. Will it affect the communication between the new LTMs and the DNS?

If so, I want to replcace the crt files of the new LTMs with the old LTMs'(/config/httpd/conf/ssl.crt/server.crt, /config/httpd/conf/ssl.key/server.key, /config/gtm/server.crt). Is this a correct methold? Or any other advise? thanks!