In order to do this, I understand that I need to bound the system so that the table change can be effectively.

Is there any workaround to avoid this, knowing that the custom table is still empty.

Thanks in advance

Not sure I understand - I add new fields to custom tables often. Never do I bounce the system. Usually I just make sure everybody is out of the sessions that use that table. And depending on the changes sometimes I do not worry about that. It is best to do it when no users are on, but depending on the change we do it anyway. In most cases we coordinate with the users to make sure they are out, install the change, convert to runtime, then let them log back in. This works for us.