Then don't follow the instructions! Lower the heat so the pan boils but doesn't boil over. Whoever wrote the instructions can't possibly know what YOUR stove is like, so use some common sense. Just follow "boil for X amount of time" and IGNORE the rest. Put it on whatever heat it needs to achieve that.
You may want to put it on the highest heat to get to the boil quickly, but after that turn it down to what it needs to keep it boiling. That almost certainly WILL be lower - the pan is hot now, so you need less heat to keep it boiling hot. Just enough to replace the heat it's losing from being in a kitchen that is cooler than boiling. How much lower can depend on the size of the pan, the size of the ring, how much water is in the pan - all of those have an effect on how much heat you need to keep it boiling.
You just have to get to know your own stove. With mine, for example, 6 is the highest setting so I need that to get the water boiling, but once it's boiling, for cooking some vegetables in it I can turn it down to 4 or even 3. That'll keep it bubbling away. For pasta, I use a bigger pan with a lot more water on a bigger ring so the pasta has room to move around and not stick together, so to keep it on a good boil I need to turn it down only to 5. You really need to work this out for yourself. See what works for YOU with YOUR stove and remember that.
Then there is a recipe I like which calls for simmering with the lid on for 30 minutes - putting the lid on keeps heat in so I find I need to turn it all the way down to 1 when I make that. It's still gently bubbling away inside and that's a simmer - so 1 is all it needs. But that's for one person, so if I make it for two and there's double the amount of food in the pan, I MIGHT need to turn it up to 2. I don't know - I haven't tried that yet!
If water is boiling, putting up the heat any higher won't make it any hotter. Once water gets to 100C or 212F, that's the temperature it will stay. Apply even more heat and it just turns to steam. So you don't need to cook for longer. As long as the water is boiling, it will take the same time.