Genetic mutations in plants
I think that the potential survival of your seedlings could more likely be credited to your care and management than random genetic mutations. While, of course, DNA mutations happen during cell replication, evolution at the whole-plant scale primarily occurs over the course of generations, not the lifespan of a single plant. You may well be able to get these trees to thrive in your environment with some care and love, although they may not grow as vigorously. Here is a link to a gardening website with tips on growing ceaders in a home garden, although I agree with the commenter that you'll get much better help at the Gardening and Landscaping Exchange!

Best of luck with your horticultural endeavors!