Yes, reissues/other formats are considered a seperate 'release'
If you go to the release group page:
And hit 'add release' on the right hand side, you can fill out all the information from your CD version, release date, barcode, packaging etc. Then it will give you the option of re-using the tracklist/recordings from the LP release (just change the format to CD after selecting that option, and check the numbering etc).
Then you're done! Should be pretty quick. Let us know if you need a hand.