How to exclude command window changes from redo (period) to vim?

I always use the command window instead of the command line.

I do it through the map

nnoremap : q:i

The problem is that the changes made to the command buffer are then written to the repeat register (I'm not sure if the correct term, please correct me).

eg. when I do :w<cr>to save the file, the next point that I give out is pasting w.

Can I somehow forget the rewritable commands created in the command window when it closes?