Following the answer of Carlos Martín I open this thread for checking this issue. I paste my original post:
"We have upgraded our 4.8 environment to the 4.12 version. We are very interested in blocking the CPU modifications done by users; we want to create a template and only allow to modify the VM capacity for vCPUs and Memory.
We have added this line to oned.conf:
VM_RESTRICTED_ATTR = “CPU”
But now we can’t modify the VM vCPU nor the Memory… This error appears in Sunstone:
[VirtualMachineResize] User  : Template includes a restricted attribute CPU."
It seems that Sunstone sends always all the parameters (RAM, CPU, vCPU…) regardless if you modify one or not.