dovecot - Jun 2013 - Zlib plugin: changing compression save level

Hi,

I have running dovecot 2.1.15 with zlib plugin enabled and "zlib_save_level
= 6" since about 2 years now
without any problems.

What happens if I now change the zlib_save_level to 9?
Should that work without any problems, or become the current saved
"*.m" files
incompatible or unreadable?

Thanks
Urban