Once you file a patent application, there are limitations to making any changes to it. Thus it is important to make sure the application is as correct and complete as possible prior to filing.
Amendments to description, claims
Generally speaking, the Description in a patent application cannot be changed or added to after filing of the patent application. The Claims, which are the legal description of the invention, can be changed, but only to the extent that the originally filed Description included the information at the time of filing.
Because of the intricacies of patent applications and the potential for unexpected pitfalls, it is best to work with an experienced patent attorney to prepare, file and prosecute your patent application.
Change in ownership
The inventor (or co-inventors) always initially owns the invention, and subsequent patent application. Ownership can be transferred at any time, however, either before, during or after filing of the application, or after a patent is obtained. A change in ownership is accomplished by an Assignment, and it is a best practice to record all Assignments at the US Patent and Trademark Office.