PIP assessment for pensioners

My brother has been claiming PIP for several years. He is coming up to 69 years old. He has multiple health issues mostly stemming from genetic problems. After collapsing in 2014 with sepsis, when he nearly died, his one functioning kidney failed and he has since had dialysis 3 times a week. The kidney was subsequently removed, so he has absolutely no kidney function. His various health conditions mean he is on a cocktail of medication. In 2014 I completed a PIP form and his claim was granted with no assessment necessary. Since then he had to have an assessment about 18 months ago, where his award was reduced. He received a reassessment form a few months ago, which we completed with 'No change' in every section. I also included a covering letter stating that his condition can never get any better, and questioning the need to reassess. He has been assessed by the NHS for a transplant and advised because of his past medical history it is not a viable option. Today he received a text message asking him to attend an assessment in a couple of weeks.
Following Amber Rudd's press release on March 4th which stated
"Hundreds of thousands of disabled pensioners will no longer have to go through unnecessary reassessments for disability benefits, Work and Pensions Secretary Amber Rudd has said today (5 March 2019).

Around 270,000 people receiving Personal Independence Payment (PIP) who have reached State Pension age will no longer have their awards regularly reviewed, instead moving to a light touch review every 10 years." I have read further details which state this is in place from spring (which is now).
Has anyone had similar experience and have you challenged it and been successful?