Yes by a certain date the majority of 'western' Blankets had the fixed hook sawn off.
It was great fun 'oilcanning' around the sky in that lovely tin armchair,I did most of my blanket flying in africa...we were only allowed 2 solos in the L13 because they were too valuable to risk with early solo pilots - and then it was straight into a Slingsby Swallow - some people found the transition from the tin armchair to the little wooden thing with no nose very difficult
One of our guys on his first Swallow flight - his feet came off the rudder pedals and when he placed them back on - he missed - and put them on a fuselage frame - he thought the rudder was jammed ! LOL
I was happy to fly the swallow because I had originally flown T31's....but it was definitely a backward step from the 'Blanket'