When you never know which primer is going to be available for a while, it is nice to work up a load with both standard and magnum primers. Just don't think you can change one for the other. Both are different. You can get good loads with either but you will find you will have to adjust the amount of powder you use. Anytime you are in doubt with any change you make, work up the load again with the change. It is the smart and safe way to do things.
There are some pistol powders that need a magnum primer in cold weather to get the powder to burn. Squibs have been know to happen with these powders without a magnum primer. I can't see that happening to a pistol when carried under a coat and only removed when you are going to use it.
When I think of carrying a pistol in the woods I think of it in a holster outside of my clothing exposed to all the heat or cold of nature.