It can change it very little on some cartridges, and a little bit more in others. However unless you are at or near the max load, it should not be much of a issue.
The best thing you could do is load some up yourself and try them. I would reduce your load a little and work back up. That way you will know what and how much you need to change your load when/if you need/want to change to the mag primers.
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