Answer: I think that because your magnolia was recently pruned the affected leaves are showing some sunscald. This can happen when leaves that were shaded prior to pruning are suddenly exposed to summer sunshine. Your tree will recover and the affected leaves will eventually be shed. I don't think the pruning will cause any permanent damage to your tree. Magnolia's are shallow rooted and if they begin to encroach sensitive areas you should be able to sever the roots with a shovel to stop their advancement. Sometimes roots will come up against concrete and turn and go in a different direction. You'll just have to periodically dig down about a foot out from your foundation and check to see if roots are there. If so, cut them off.
Best wishes with your landscape!
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