Can I use colder spark plugs?

Before I ask my question I want to you know in what situation the car right now is. Currently my 2005 5-speed RX-8 with 50k km is not running because the last time in November when I drove and hit high RPMs the check engine light went on and when I diagnosed the error it was P0302. Now the last time I started the car, I feel and hear that the engine is running very badly or like with a weird noise. The engine somehow runs in a sluggish rhythm especially when I try to start to motor. Its now a month since I started the car.

My Plan is to change the whole ignition system. I will put in the AEM RX-8 Ignition kit, change the starter from 1.3kW to a 2.1kW. Change the battery to a power bull one and change the spark plugs. Now my question was originally if I can use colder spark plugs then the OEM ones from NGK with Trailing 9 and Leading 8, to NGK Racing Competition 10.5 and 10, because I always like to drive at higher rpms when engine is warm enough or is this a bad idea and should I stick to the OEM ones?

I bought the car 2023 in October and I was really loving it. Soon in march 2024 some starting problems occurred, I thought the battery was failing because the car had ones no more electricity. When I changed it, the start problems were gone for a while but came back soon. Especially when I do it after fuelling or warm starting, the car always takes longer and sometimes doesn’t want at all. From what I know from the seller is that the car had an engine failure in the past and he replaced the engine with a new one (same model) and has now about 50k km as I said. As my friend suggested I also do premixing and fuel the car with high octane fuel to maintain a longer living engine. Anyways besides the engine replacement from what I know is that he didn’t change the ignition which is why I think that it is not compression loss because the engine is too far away from being already in such a state. But I may be very wrong here, let me know what you think guys.

Thanks for reading.