It's OK to shrink files if the reason they've grown isn't likely to be repeated. This is indeed the case in your situation - somebody set the database to full recovery but didn't schedule any log backups.

There's no need to change the recovery mode to shrink the logs. Just take a full backup, shrink the logs to the maximum size you think they'ill need, take another full backup, and check that you have transaction log backups scheduled at a suitable frequency.

John