No. I doubt that there is any real harm. The paraliminal work great if you use them with headphones, with intention.
If you have them running in the background while doing other stuff... they can become annoying.
Even advertisers know that if they play their ads too long the consumer shuts them out. Thats why even coke makes new advertising regularly. It like being told to do something over and over again (nagging) we often get to the point were we turn 180 degree against the good intention of our parents. Later we admit they were right but at the time they told us so often we just wanted to shut it out 
So the only problem with running paraliminals constantly is that you're likely to get fed up with it sooner rather than later. Give it a break from time to time and do use them as recommended on the covers.
PG and MS you use once a say for about a week and then once a week or as needed. Some people may desire to use them once daily for a month or 2. That's fine more isn't necessarily better. The beauty of paraliminals is you use them and then notice what happens. Changes can be subtle or great. So it helps to keep a journal as to when you used a paraliminal and what your intention was (expected outcome). Then just notice the gentle appearance of the desired changes.
I know many of us would like to see real changes over night yet if they really did happen overnight we wouldn't be able to handle them.
Just ease up.
Alex
