Hi Sanjay,
One more question:
do you mean changing 'account assignment category' or just field 'General Ledger Account'?
I suggest the following notes:
1815974 GL account is assigned even if no customizing entry
1651167 GL account default is not set correctly
Usually, GL account will be determined from customizing if you defined this, and account assignment category can also be taken from default settings.
However if you manually change them in SC, they should be changed accordingly, not revert back to default value.
Best regards,
Ivy