Can a new category of invention be added in a reissue application?
Yes, a new category of invention can be added in a reissue application, but it is generally considered broadening the invention. The MPEP states: The addition of process claims as a new category of invention to be claimed in the patent (i.e., where there were no method claims present in the original patent) is generally considered as being a broadening of the invention.
However, there are exceptions to this general rule. For example, if the reissue application adds limitations to a process of making the product claimed in the original patent, it may not be considered broadening. The MPEP provides examples: (1) a process of using the product A (made by the process of the original patent) to make a product B, disclosed but not claimed in the original patent; or (2) a process of using the product A to carry out a process B disclosed but not claimed in the original patent.
To learn more: