There is no simple answer to your question, as there are too many variables. Generally speaking, the ECU does have the ability to adjust fuel trims and other parameters enough to run a good intake and a downipipe and still keep AFR's safe, although not optimal. There can be some leaning out of AFR's that can be a little concerning when under full load at higher speeds. That's why AFR's do need to be monitored in some manner.
However, in my personal experience in a warm and humid climate (south Mississippi) the ECU seems to be able to keep things reasonable and safe without a tune. In cold air in what passes for winter here, I sometimes get fuel cut (rarely), which is a built in safety feature I am willing to live with in the winter.
My most important concern is not the ECU adjustments but rather the possibility of boost creep, which is a function of the wastegate on the stock turbo not being able to bleed off all the potential boost because the wastegate port is no longer big enough to handle the extra flow from a larger catless downpipe. I can see the boost spiking to 18-19 and then being quickly dialed back and held to 16 psi under high load high speed conditions, so I conclude that under my particular driving conditions, I am not getting boost creep, only controlled boost spike, which is not unsafe.
