You don't need to use programming for this task. You need to create an object replacement (in your example, an Account object replacement), in which you can set the default value for the corresponding columns, save the changes, and publish the object.
After that, when you open the pages of creating records, you will see the fields immediately filled with the default values.
These links can also be useful for you to find more options for achieving your goal:
1) We can not utilize the generic default value, becasue depending on the conditions the Type, might have differnetvalues.
2) Our frontend logic is associated with OpenSelectionWindowRequest. In the documentation of OpenSelectionWindowRequest there is no documentation for default values.
If you need to use a value based on one of the fields of an object, it is fashionable to use business rules at the object level, which, depending on the value in one field, will set the value for another field using the “Set values” option.
