You cannot retroactively change your license for already published code. Previous releases remain available forever -- that is part of the "contract" between the "publisher" of code (here, you) and its users.
You are of course free to re-license new versions.
And CRAN is equally free to refuse to distribute commercial code. Because if you look more carefully, you will note that the 4600+ packages on CRAN are all Open Source and not commercial.