[GNC] How change Trading split

[Fred Tydeman]

I am using GnuCash 5.12 on Fedora Linux 41 on Intel x86_64
I have some stock transactions with trading splits.
I try to add another split (for capital gains) and alter the Trading split
$ amount
(to the Basis price).
But, I endup with an Imbalance-USD split and the Trading split back to the
original $.

I have also tried deleting the Trading split and the Imbalance split and
clicking on Enter.
Both splits come back.

If I turn off Trading via File: Properties:
delete all the Trading splits,  Click on enter,
then turn back on Trading,
and then run: Actions: Check&Repair: All Transactions
I end up with the correct set of splits.

What is the correct way to do this?