I would suggest to embrace SAG Update Manager for fix management.
Features :
Backups : Update Manager will backup your files before fix update. However always take a file system backup as a fall back.
Roll Backs : Update Manager can roll back fixes (and you have your file system backup in worst case)
Fix Images : Create Update Manager Image and you can keep appending to that image every time there is an update. The update manager will update itself everytime if configured to do so. If you are using centralised image then you can create 1 image and spawn it to all update manager installations
Keep the Update Manager installation directory separate from your webMethods installation directory. This helps in taking file system backups of the SAG Update Manager itself.
Note : Update Manager does not support roll back for some MWS fixes. In that case you should rely on file system backups including MWS Database snapshots.
I recently installed Core Fix 13 on one of our IntegrationServer using webMethods 8.2 UpdateManager, but things went wrong and i have to rollback the fix to an older version(Core fix 11 - was installed before Core fix 13).
Please suggest if i can roll back the fix or do i need to first uninstall it and then have to install the Core fix 11.