If I change the bulb from 6000K to 2000K and use t...

2000k might be too "warm". Other wavelengths are still important and not just the red ranges. The other thing to consider-- plants adapt to the light the receive. So the pigmentation and such adapts to CCT and intensity. If you drasticalyl change the light provided, that potentially has some drawbacks if you do it midstream... probably small effects that are diffiuclt to see with eyes and not tracking large samples while freezing other variables and having a control group for camparison to make a rational assessment on such a thing. Don't over think it. 6000k and 2000k are probably both too extreme regardless of whether you use them in vege or flower and the effect of it is virtually impossible to recgonize with your eyes. no matter what, some reconfiguration over time will occur in the leaves and that has a cost of 'something'. wehther it is outweighed by some other benefits is not something any human can resolve by simply doing it with a few plants in their home and wildly variable environments etc. these people are just lying to themselves and reinforcing existing long-held beliefs regardless of shoddiness of evidence used. like mouse said, focus more on providing proper levels of DLI and then play around with CCT options after that need is met.

Yeah going from MH to HPS for flower is perfect. Plants life cycle wants white light seedlings then blue then red in flower...

Hi yes the switch to 12/12 is OK but the most strains in the flowering phase, need around 60,000 lux. It is important that the light source is not too close to the plants to avoid burns. You can use the app Photone to adjust your light I usual use in flower an PPFD value from 900 to 1000 µmol / (m²s).

Yes, if you're planning to switch to 12/12 for flowering then it's a good time to switch your bulb to the red end of the spectrum.