Welcome to
I have seen that mod done but I have never done it myself
good luck with it
You will have to start by taking the SAK apart and make note where everything goes
Next you will have to take the Spyderco blade out and then grind it down to match the tang of the main SAK blade, then you may also have to grind more off the Spyderco blade (probably around the choil area) for it to be able to sit correctly inside the handle
Again, I have seen this mod done but never have done it. So, for sure, grind some then check often because you can take material away but you can't add it back