Hondata

My car EG civic with B18c1, turbo kit, 550 injectors.

I am planning on upping my boost beyond the limits of my stock map sensor. If I buy a 4 bar map sensor, will I need to re-tune everything, or will it just work up to where my map sensor ran out of capabilities (10psi and above and tune from there), or will I have to re-tune everywhere?

You should not have to retune. Just continue tuning the high levels of boost that could not be read before.

work past where your map sensor ran out of capabilities (10psi and above and tune from there)