Help downgrading and keeping sw version

[zurdo002]

hi I'm a noob on this kind of topic, but i'd like to know if I do a downgrade to 2.2.1 after I updated to the version 2.2.2 and the SW version to ms690zv7, will it keep the SW version or it is going to downgrade to the version ms690zv4 that i used to have before? I'm asking this because I was wondering that only the SW update solved the problem of the random reboots of the phone. that way it wont be freezing and rebooting and the phone will be rooteable