The Bosch MEVD17.2.G ECU used in the M2 is pretty sophisticated and when flashed with another program, even if it's done by a dealer for standard repairs, there is incremental number that increases and is saved, within the computers reserved EEPROM, i.e. permanent memory. Tuners refer to this as a "flash counter."
All a BMW claims rep has to do is refer to that number and extrapolate, as confirmation that the vehicle's software was rewritten, then they'll refer to the boost logs, timing, AFR and measure them against the set stock variances, as conformation of their suspicion.
They will allow for some fluctuations in the readings but if they see a major spiked in variations, it will be noted and possibly be use as evidence of tampering, thus, denying any hypothetical warranty claim.
Also, the ECU itself, if it's set programming determines something is out of bounds, for a reasonable period of time, like let's say the boost pressure and AFR abnormally spikes, from the stock parameters, it will assume the original programing was changed and record a tamped code
201101 DME: Protection against tampering: Program or data manipulation detected.
The fact is, the CS tune is mild and probably is safe but you have to circumvent the vehicle's software firewall to install it, which will leave breadcrumbs, making you vulnerable to warranty claim denial. It's kind of a quagmire but it's the risk you take for more power.
Now, if you don't care about the warranty coverage and just want to a tune; it's your car, you can do whatever you want to it but that also means you disclaim BMW from a potential warranty issue.
https://f80.bimmerpost.com/forums/sh....php?t=1318465