Many icing limitations (ours included) specifically prohibit entry into cloud when it is snowing for exactly this reason.
Now, on the icing topic, what do you think about the generic icing limit "flight into known icing conditions is prohibited" ?
You can enter a cloud in freezing conditions but
may or may not get icing on the helicopter, you will never know about the ice until you are inside the cloud.
As I understand you need to avoid that 'below 0C' cloud as far as possible or enter it only if you have enough altitude below in case you encounter icing.
regards
Aser