Nvidia was quickly forced to cancel their decision about blocking OC:
https://forums.geforce.com/default/topic/805791/geforce-drivers/gtx-900m-overclocking-with-347-09-347-25/post/4466443/#4466443
https://forums.geforce.com/default/topic/805791/geforce-drivers/gtx-900m-overclocking-with-347-09-347-25/post/4466443/#4466443