You are limited with what can be done, as you need to retain the secondary exhaust valve. If you change with diameters too much and affect how the turbos spool, you can also get into code 66 territory.

I think there are some aftermarket ones that exist, that retain sequential, but most you’ll find delete the secondary exhaust valve and are designed to convert the car to twin parallel. So just be mindful of that.

Generally speaking, don’t. Don’t mess with too much, the sequential system is moody and susceptible to changes like this causing issues. It’s safer just sticking to cat-backs etc.