I have been using "green stuff" for years to mold housings for electronic jacks & such. IMHO it will not stand up to the forces needed to support a knife blade in our typical use. But for field use, it is a great medium speed 2 part epoxy. I keep a small piece of "green stuff" in my BOB. Have for years. But, replace it every 6 months or so. It gets dried out and does not mix well after that.

Instead I suggest getting a blade holder from any animal feed store. Look for a stainless steel scalpel holder. They will also have a large assortment of various blade shapes. Just "snap" on the one you want. I carry several blade types and two handles in my large first aid kit. You could cut a handle down to fit your kit. Be aware that not all blades fit all handles. Different brands and sizes.

You can probably also find disposable medical knives with plastic handles and various blades. But the blades are fixed, not interchangable.

For the small weigh penalty, I prefer the stainless ones with several blades. Have used them many many times for "minor surgery" in the field. Handy for general use as well.