As I mentioned before, the warped space-time is described by Aerith how things are within the Spiritual Energy, there's no mention of the Lifestream actively doing it nor of a consciousness being behind the phenomenon. She doesn't say "the Lifestream is changing the concepts of time and space" she says "the concepts of time and distance are different in the world of Mako".
Even if we go with the idea that there is a consciousness, the Cetra could communicate with the Lifestream to borrow the powers of the Planet in order to use Magic and how that is the same process to use Materia, which borrows the knowledge of the Cetra, if we go with the idea that only the Lifestream knows how to use its powers.
Thing is, Mysidian mages are not average users of magic, they are erudites, scholars dedicated to researching and developing magic in a town of spellcasters. Using the example you gave, they are not an average user, they would be like a computer engineer with a PhD on the subject.