Restructures are rarely challenged on whether they were necessary. They are challenged on whether anyone can show how the decision was made.
Write down the reason, at the time
Not a memo for the file. Two or three honest sentences about why the structure is changing and what problem it solves. Written before the decision, not reconstructed after it.
If the reason is hard to write down clearly, that is worth noticing. It usually means the decision is really about a person rather than a role, which is a different process with different requirements.
Keep the selection visible
When some roles go and others stay, record how you chose. Whatever the criteria are, write them before you apply them and keep the working. A decision that can be explained is defensible. A decision that has to be remembered is not.
Nobody keeps a record because they expect a claim. They keep it because a year later nobody can remember the reasoning.
Consultation is a conversation, not an announcement
Tell people what is proposed, listen to what they say, and keep a short note of both. If someone suggests an alternative that you reject, record why. That single line does more work than any policy document.
Say the same thing everywhere
The version in the meeting, the version in the letter and the version told to the rest of the team should match. Most disputes about a restructure begin with an inconsistency that nobody intended.
Practical steps
If a change is coming in the next few months, start the file now. The reason, the criteria and the dates. It takes an hour and it is the only part of this that is hard to produce later.