It's okay to make the substitution.  It's not okay to make the substitution without reducing the powder charge to start until you find out whether the magnum primer requires a lighter charge than you could shoot with the standard primers.

On a side note, I wish y'all would use the search function as it works fine in this forum or peruse the first 5 or 6 pages of the forum before posting redundant questions.  This question has been answered eleventy billion times in the last 24 months.