Changing Revenue Recognition Plans

We have a number of items in our system which have a 9 year installation revenue recognition plan, so the revenue for these is recognised over 9 years.  This has always been a historical thing but we are now looking at changing this so that installation revenue is recognised over the length of the subscription instead.  Therefore we will need to alter the current revenue recognition plans in existence.

Ideally what we would like to do is to adjust the plan so that the remainder of what has to be recognised is done so over the remainder of the revenue plan (adjusted to be the length of the contract rather than 9 years) but the difference between what has already been recognised and what should have been recognised had the plan been shorter is posted in Jan19.  For example: