no, using the mag primers will not run the pressure over a +P level.
i have replaced small pistol with small rifle and lg pistol with lg rifle and vice-versa in working up some loads, with no dangerous results.
i have used bullets cast for .380's in 38spl , 357 mag , 9mm bullets in .380's , .357 mag and other swaps like that without incident either.
if your careful and look at the specs carefully and study the loads given, you can create something fun and usable ,that is safe.
its just my opinion, but i think it makes you a better hand loader. you teach yourself an understanding of whats going on in making up a specific cartridge.
and i got a better understanding of each component and thier uses and limitations.
as an example i took a .357 mag case, used a 90 grain cast bullet for a .380 ( .355 dia ) and set it on 7 grains of titegroup, i cut the case back so there was just enough room for the powder and bullet. i got fair results with small pistol primers, but when i switched to small mag primers it really preformed well.
it makes a great gallery load.
but that's me, i find tinkering and experimenting with loads fun. but being careful and safe is paramount. only do what you feel comfortable with