I could be wrong here, but if i remember correctly, each SIM update includes a MIB update so there is a chance the upgrade will reset anything you've changed as far as severities, filtering, etc. Basically, the MIB file is replaced/updated and imported again so I believe the changes are lost.
I only mention this in case this was your main reason for not trying a clean install - in other words, it may not matter.
I recently upgraded to 7.4 but haven't checked to see what got reset just yet as mine isn't in full production.