The CMG1 is for emarker Cable application, the answer of your question is no. You cannot write the firmware for the CMG1 and program it.
The CCG2 CYPD2103/CYPD2103 is for e-marker cable application, the answer of your question is no. You cannot write the firmware for the CMG2 E-marker, since CCG2 E-marker cable is not released in SDK.
If you just designing a captive cable of type-C in your design, you can make sure what's roles you are going to design, and then select CCG3,4,5,6,or CCG3PA, those part number have SDK and can be customized by PSoC Creator.
I want to make an electronically marked cable. What does "costumizing" mean? Can I not freely programm it?
I need for example some GPIOs for LEDs, buttons, I²C for a sensor or maybe a small I²C display.
I want to show some text on display and I need programm it freely.
Can I make it with CCG3/4/5/6 chips?
If you want to make electronically marked cable and need for example some GPIOs for LEDs, buttons, I²C for a sensor or maybe a small I²C display, Cypress CCGx device can meet your requirements. But the firmware example do not have application for electronically marked cable based. You can use Notebook, monitor and so on example code and coding the firmware by yourself to achieve it.
But for Cypress mature solution, CCG2 CYPD2103 and CMG1 CYPD2703/4 is for electronically marked cable, but the firmware is not opened, so that you cannot add the I2C/GPIO based on those reference design.
Ok, thanks for answer.
Do you know how can I write programm for CCG3? Is there SDK, compilers, IDE? Is there any reference design for software?
And what can I read over I²C? Where can I find the register descriptions of the device?