Yes, you can replace the ECU. It's just that most people who buy these cars expect to get a great car from Japan thats been put together properly and will have no issues. Sadly thats often not the case. There is 2 very opposing approaches to tuning cars over there. You get your no-expense-spared cars, which are few and far between, but when they come up they really are proper, but you also get your shonky shit, which really is shonky.

We love PowerFC ECU's, you're looking at around £1000-£1200 for an ECU supplied fitted and mapped and including the Commander (Monitor display for in-car info). They are plug-and-play and extremely good for the money.