LMDE6 change default gcc to gcc9

quite and fast question .... linuxcnc work quite well ... now need to dowgrade to gcc9 from stndard gcc12 .... can i have some problem compilingf for example a new custom kinematics? 

Ask these because sees all new kernel request for running linuxcnc 2.9.1, 2.9.2 and 2.10 have as default minimum gcc10 ..... and never try install lcnc 2.9.2 in a system with less than gcc9 .....

regards

just done ..... prerequisite a lot of patience, because seems is not so simple change apt on LMDE6 rt-preempt ... or alwais not in my version downloaded at febrary 2024 and the upgraded to kernel 6.6 ..... any how set as default gcc9 all still work whitout problem. For sure if need to compile and install something of new (like app or libs) need to reverse to default old gcc12 .... these for system sanity ....
regards