[Klesk]

I was reading over FFXI Wiki page and it just says to revisit the Marble Bridge if one decides to drop their CoP ring to get a new one. Will I have to fight Promathia again almost like Divine Might a second time?
Am I able to drop the ring as is and just get a Rajas Ring without fighting Promathia?

[Kagemitsu]

If you're tossing it for the first time, you can grab another ring at the marble bridge right away. If it's the second time, you have to fight Promathia again.

[Klesk]

Ok great thank you

[Fargo]

You don't have to fight Promathia again.

* If you discard your CoP ring, you will be able to obtain one of the three rings by revisiting the Marble Bridge. If you happen to drop the ring the same day as obtaining it, you will need to wait until JST Midnight once again before the cutscene will play. If the ring is discarded again, you must wait 27 real life days before you will be able to once again choose and obtain another ring.
* If you have discarded your CoP ring for a second time you MUST check the Marble Bridge door to activate the timer.

Quoted from FFXIclopedia.

[Prothescar]

You should never have to fight Promathia again. All you have to do is discard your ring and go to the Marble Bridge for a new one.

If it's the first time you're switching the ring you can just drop it and get it back right away.

If you've dropped it before you have to wait 30 days from the last time you dropped it. I.E. you drop it on January 1st you can get a new ring on January 31st.