You can’t just “add Gore-Tex.” It has to be seam sealed, and the material it needs to be laminated, then sealed to at hems needs to be at very least 30% polyamide to get it to bond; Mackinaw wool contains 0% nylon. To add zippers requires that you have extra fabric that matches the rest of the garment (weight, thickness, and appearance), same with extra pockets (exclusive of the pocket bag- which can be made from anything). About the only feasible part of your plan is to add grommets for u defrost straps and snaps at the cuff, tho Mackinaw is very thick and you’ll find it is bulky when crimped or folded and if the snap isn’t particularly hard to snap/unsnap, you’ll find it won’t stay shut. Long story short, these are the reasons Rainy Pass won’t touch it. You should probably just look for a product you want in the first place as opposed to literally trying to transform one product into another one. Will be much easier in the long run. Also, for what it’s worth, these pants would be pretty (probably too) hot for any kind of aerobic activity.