After the fire at Hercules in the early '80's, 2400 was indeed changed, and is "hotter" than Elmer's earlier version. I have shot some cast 158's with 13.5 gr. of old 2400 in a .38 special case, and it was damned hot. I never shot heavier bullets with that load, so can't comment. Bear in mind that Elmer and Skeeter used bullets with crimp grooves that allowed them to be loaded "long".
I later switched to 12 gr. with a hard cast 158 & new 2400 in .38 Special cases and it was / is very satisfactory. Still warm.

I don't believe the load you suggest will "blow up" your GP 100, but personally, I would not be inclined to use it except in a FA 83 or T / C. But it's your gun ....