I would like to know if it's possible to change service account used by WSUS 2008R2 SP1 to sync with Windows Update servers
No.
Lawrence Garvin, M.S., MCSA, MCITP:EA, MCDBA
SolarWinds Head Geek
Microsoft MVP - Software Packaging, Deployment & Servicing (2005-2014)
My MVP Profile: http://mvp.microsoft.com/en-us/mvp/Lawrence%20R%20Garvin-32101
http://www.solarwinds.com/gotmicrosoft
The views expressed on this post are mine and do not necessarily reflect the views of SolarWinds.