Q: If I string using a hybrid, should my mains and crosses be strung at the same tension or can I use different tensions?
A: This is a question that comes up pretty regularly, especially since hybrid stringing has become so popular at all levels of tennis. The simple answer is yes, you can absolutely string your mains and crosses at slightly different tensions, though I strongly advise against using drastically different tensions. If your heart is set on experimenting with different tensions for mains and crosses (which is totally fine if that's something you want to do), my advice would be to keep the tension for your mains and crosses within about 3-4 pounds of each other.
The reasoning behind that recommendation is all about minimizing uneven stresses on the frame. Most players who've been playing more than a little while—or who have been keeping up with the Ask the Stringer column—have probably heard that once they break a string, they should cut the rest of the strings out to relieve the tension on the frame. That's because when a string breaks, others around it loosen up too, while others farther away from the break remain under tension, resulting in a frame that is unevenly stressed. Leaving a frame like that over time will eventually distort the shape and damage the racquet.
Similarly, stringing the mains and crosses at radically different tensions will exert uneven forces on a frame and cause distortion that will damage and destroy a frame over time. Once a frame becomes distorted, the damage is often permanent and your frame is toast.
So, circling back to your original question: yes, it is fine to experiment with slightly different tensions with your mains and crosses, but it's important to keep the tension differential to a minimum to protect your frame in the long term.