I have worked with balloons to create many forms of armatures for a few years now. I use them as they are (blown up) standard & creatively shaped ones. I often cut into the dried PM'd balloon shells as i call them to create either new shapes from the whole shell or bits of said shell.
Now even though as i say i have done this for a few years now even i make mistakes, not directly of course a room can unexpectadly become too cold or too warm overnight. A cold room results in the balloon shrinking & if it does this before the PM shell(s) are dried enough to retain the final desired shape. Well theres not a lot you can do unless you are extremely creative lol.
Of course this works the opposite way if the room becomes too hot too. Below is a nasty looking rupture that actually occured 'after' the shell was fully dried. Sadly i mis-counted the layers & the built up pressure in the balloon was actually enough to cause the damage shown. Trust me it WAS worse than it looks in the picture.
When this happens there is no need to panic what so ever, this IS an extremely easy fixable problem.
First allow the balloon to cool down by placing the whole thing i a cool place for a while. It will be obvious when enough is enough. Quite simply when you can squeeze the split together again easily then it's ready to be repaired.
Depending on the size of the balloon shell, apply two layers of maksing tape in a cross over fashion. By that i mean go in one direction with the masking tape then another 'opposing' direction with the second layer, just like you would with paper strips.
Now rub it all down with a smooth but hard tool. I nomally use the finger guards on my scissors. Next string up the balloon in it's original drying place in a warm room to allow the balloon to re-inflate. Once the balloon is visably filling up inside the shell again quickly add around 4 to 6 layers of paper strips. Then return to your chosen drying place & leave overnight.
Once fully dried again you will have a fully restored balloon shell to work with.