FIA is just a bunch of incapble idiots, i agree you dont change mid season rules this is the same as with the double diffuser, some teams are clever and always will find loopholes or workarounds to gain those few extra tenths. In the end its the same for everyone so why not leaving it as it is?
What you get now is that Mercedes can use 10% off trottle, Mclaren 20% and renault engines 50% and all other teams are 0% ,..... whats unfair now then xD Withing called a meeting with the workgroup so will see what the outcome will be.
In my opinion they should stick with their decision, no off trottle means no off trottle and if that means renault engines will have a reability isue then thats their problem, they knew for a month that the rules where going to be changed right!