Is high altitude bad for aortic aneurysms?

Depends. This is a difficult one to answer. The changes that may occur at high altitude, such as relatively less oxygen may lead to increased heart rates, especially with exertion, and that is an undesirable effect. However, more details are needed: location of the aneurysm? Size and the etiology of the aneurysm? M how far above sea level is your location? What would be a rate of ascent?
Yes, it can be. Traveling to high altitudes can raise a person's blood pressure, depending on the rate of ascent and the amount of time spent at high altitudes. At higher altitudes, the body works harder to process oxygen. This extra stress can raise blood pressures. A person with a large aortic aneurysm may be more likely to rupture if he is not acclimitized to the higher altitude.