Frank,
No, you don't need the CNTL_ functions for changing channel.
You quite often need to use a delay between commands in a macro to a STB including channel changes.
I am currently preparing some web pages which will include a table for the CTNL_ functions, but they have different functions depending on the STB you are using, but control such things as PLAY, STOP, RECORD NOW etc. As previously stated if you press menu for STB, then the feature for your STB have numbers by them which are equal to the CNTL_ numbers.