The boost pressure is controlled by a dedicated calculator in ECU, then changing the spring is not clever and maybe dangerous (for reliability). The spring force have to be fitted in accordance to pressure mapping of calculator and help in transition periods only!
Not sure about this at all. Did similar on old SAAB 900 T16s but that had little ECU input c/w RS2 and still Abbott racing had to spend time to set things up.
David I found Scott at AMD very helpful over the phone and his only advice for my car @77k to ensure consistent boost was to replace the diverter valve Bosch p/n I will check if interested but same as porsche 944 turbo
I wouldn't play with the spring - Tuners will put in a stiffer spring and adjust the pre-tension on the spring but that should only be done along with a remap to account for it.