You won't break log shipping... have a look in BOL at Log Shipping Role Changes.

Essentially, you do your final transaction log backup at the primary using "WITH NORECOVERY", then

restore this backup at the secondary using "WITH RECOVERY"

Your secondary is now acting as the primary, so all the backing up and restoring of logs is reversed. When you are ready for the primary to assume it's original role just do the reverse (backing up the secondary WITH NORECOVERY etc).