The initrd file is the "initial ram disk" which is used to load the drivers necessary to boot the system. It's built based on the kernel version and the /etc/modprobe.conf file to load those drivers so the system can fully boot up.
Sorry about the version numbers; I grabbed the wrong one from your post. It's safe to backup the initrd file that is there, and rebuild it. Putting the old one back is as easy as renaming it back to the original name.
Here's a safer version:
cp initrd-188.8.131.52-18.fc9.i686.img initrd-184.108.40.206-18.fc9.i686.img.bak
/sbin/mkinitrd /boot/initrd-220.127.116.11-18.fc9.i686.img 18.104.22.168-18.fc9.i686
This will not prevent the working 22.214.171.124-14 kernel from booting, because it's only associated with the 126.96.36.199-18 kernel. If there is any problem at all, you just need to put the original back in place:
mv initrd-188.8.131.52-18.fc9.i686.img.bak initrd-184.108.40.206-18.fc9.i686.img
If it makes you uncomfortable, I would suggest just sticking with your working kernel, unless you are running into a problem that you think the newer kernel would solve.