You can take an image in LR4 and open it as a SO in CS5, but you better have the ACR 6.7 RC installed if you are using PV 2012 in LR4. Also note that ACR 6.7 can RENDER PV 2012 but you can't make any changes to the adjustments in ACR 6.7. That will take ACR 7.x in CS6. That makes using LR4 and ACR 6.7 less useful...
thanks for your fast answer !
But, if I understand you right, it makes no sense to use Lr4 -> ACR 6.7 to render SO becasue the sense of a SO is ( to my mind) that the raw is included and can be changed any time with ACR.
What I don't understand neither is that Adobe deosn't offers a way back for the SO -> raw to Lr. This could help.