Sure!
Open up a new Journal Entry and hit Correct. Follow the prompts and find or key the JE from last month selecting Back Out and Correct. When done, you'll have 2 JE's, the backout entry and the correction entry. Delete the backout JE. Now all that you have left is a correction JE that looks just like last month's entry, has today's date and will let you make changes.
Easy enough. Just don't forget to delete the backout entry!
You, Me and Dynamics GP