Unfortunately, no, this is not possible, and here's why:
Mantis allows you to highlight individual words. This is highly desirable for Bible studies like Precepts, where you need to highlight, say, verbs in one color, etc. You can highlight different phrases in different colors, too, in any combination.
With this flexibility comes a price, and that is that highlights are tied to a translation (what we call a "volume".) This is because each translation has different words, and sometimes things are completely different. Words may not even exist in one translation that are in another one. So it would not make any sense.