I am wondering if you think Royal protocol matters?
Yes it does - it means that people know what is expected and how things will run. It is however a continuously evolving thing, and it's wrong to consider it set it stone
For example the Palace have emailed inviting Harry and Meghan to the Coronation instead of sending them a formal printed invite. So do things like this really matter?
There have always been informal exchanges about diary matters and invitations, by letter, then by telephone and now by email. It's not supplanted the actual engraved stiffie of the formal Invitation. It's simply how the co-ordination is done
Does it matter what clothes they wear for example or should protocol be adhered to with that?
Yes, because they need to dress for the part. What that means in practice depends on what they're up to. But it could be suit or uniform, day dress or ballgown, no hat, hat or tiara. Bright colours so they can be seen by crowds. See-thru umbrellas for the same reason.
Can protocol be changed?
Yes, always has always will.
Charles is changing tradition with what he wears for the Coronation
Each monarch decides for themselves and twas ever thus.
Kate has worn a dress that is off one shoulder
As did ER II and Diana Princess of Wales before her - indeed they have both worn strapless
So do the changes matter?
Not really, because it's always been changeable