My experience has been that almost any bulk change to the configuration (import, import XML, push) causes and interruption to sessions on the target machine. I'm hopeful that 6.2 makes it better. From the 6.2 "What's New" document -
Streamlined Management - XML Import/Export and Push Configuration
Version 6.2 adds additional functionality to the existing XML Import/Export and Push Configuration features, completing support for all SSL VPN policies. Additionally, these functions have been improved to minimize restarts that can result in service impact.
Allows administrators further granularity in deciding which policies to synchronize between disparate devices or clusters.
Allows administrators to make configuration changes via XML Import and Push Config without worrying about service restarts, allowing greater management flexibility without any user impact.
Available on all Secure Access products.
Like a number of others on this board, I like to let a new version "cure" before I use it, so I would not recommend jumping on 6.2R1 (6.2R2 is not so far away, anyway). But I'd recommend you check on this board for others' experiences with 6.2R2 before deploying it. You might check with your SE to see if you can get details on this improvement.