From the project description:

Hundreds of thousands of decisions are made annually under the Immigration Rules. Decisions which can be life changing for those seeking entry or leave to remain in the UK and their families.

But the Rules are widely criticised for being long, complex, and difficult to use. On 1 May 2017, the Rules totalled 1096 pages in length and their drafting is poor. Many provisions are duplicated, cross references are often incomplete and some parts are incomprehensible.

Our project will not involve any substantive policy changes or any new legislation. It will instead aim [to] redraft the Rules to make them simpler and more accessible to the user.

The review will not impact the legal basis on which a person has leave to enter or remain in the UK.

I think they mean “affect”.

As background, the Law Commission is a non-political independent body, set up by Parliament in 1965 to keep all the law of England and Wales under review, and to recommend reform where it is needed.

The Law Commission is also looking at “administrative review” in a general sense, where “public bodies look again at a decision when someone complains that they have been treated unfairly by a decision.” This will presumably include looking at the Home Office system of administrative review in immigration cases.

Source: 14 new areas of law set for reform – Law Commission