But can we modify and rename the second brush, asking as I truly don't know? If we can change the second brush, meaning the copy of the first, doesn't it become less important to modify the original brush?
I believe the second brush can be accessed and modified.
Your point is valid - modifying the first brush may often not be as important.
I have situations where it does matter: Suppose I made a mistake with the first brush - I can't correct it unless I can access it.
There are many instances when the first brush (used for softening a BG), isn't strong enough. With LR4, I start a second brush at a different location - now they are both accessible. However, the second one takes as long as the first one - a lot of extra work.
If in LR5 the first can't be accessed but needs fixing, the only solution I see is to delete both brushes and start over. In some cases this is not tragic, but I've been using the brush to soften the BG of flower closeups/macros - on a complex flower this can take some considerable time - I don't want to have to start over.
It could have been so useful.