You can go to the RTA website and inquire as to which plates may be available for your car, according to your preferences. That is how I obtained my plates. That was some years ago. When I did my original inquiry, SEL 690 was available, as well as the plates that I chose. Maybe SEL 690 is still available. Unfortunately, the RTA now wants an annual subscription.
I don't think I would now be motivated enough to want customised plates, if I were required to pay a subs. If I was now asked to pay a subs. or surrender my plates, it would be 'no brainer' for me, I would surrender my existing plates. That would be a shame.