For me it would depend what livestock I have and whether I have sump.
No livestock - I would swap everything and restart cycling.
Livestock and sump - I would gradually move current rocks into the sump over a week or so, then add new aquascape in DT, then remove rocks from sump gradually 20% per week, while dosing bacteria.
Livestock and no sump - I would probably gradually pile up current aquascpae to one corner, add new aquascape and gradually remove 20% of old every week while dosing bacteria.
If current aquascpae is big I would break it up first at the glue etc gradually over a week or so, only few pieces at a time and rinse them with saltwater at the breakage before putting them back in, then pile them into either sump/corner of DT as above.
Would stop at any sign of ammonia and wait until things do stabilise, keep dosing bacteria, then continue.
Mind you if you put rocks into the sump from DT/change old aquascape around, stuff might die on old rocks, so some ammonia spikes are expected.
OR
If you have sand and a lot of media in sump and you dont want to mess around for weeks, you can also attempt the whole swap at a single go, add bacteria, and hope biofilter in sand and in sump media will hold up.
I would probably go with this latter, I assume in a 3 month old tank you will only have hardy fish/corals, so they will likely survive a mini cycle (have some triage at hand).