yes assuming you hit flash clockworkmod recovery from rom manager, if you hit apply sdcard:update.zip, this will take you into a green recovery page,
From here you should do a nandroid back up ,
then wipe data/factory reset
then wipe cache partition
then go to advanced>wipe dalvik cache
then go back
then you scroll down to install zip from SD card
From here you should do a nandroid back up ,
then wipe data/factory reset
then wipe cache partition
then go to advanced>wipe dalvik cache
then go back
then you scroll down to install zip from SD card