Lawrence is SSOO right about the liability, trust us, most of us have been and/or are welders. And I have owned my current welding business here in AZ for 20 years now (WWOOOWWW!! Yes, it has been that long!).
Making some extra/side money is great, but watch your backside because everyone else is trying to bite you there.
Now, Lawrence, I hope this is just in the wording: you don't need a SEPARATE WPS for every joint, though I am definitely not one who advocates a one size fits all approach. But there are many that can be grouped together all other things being within proper Clause 3 parameters. And positions, take a good look at the commentary for D1.1, as well as other materials provided through the bookstore for preparing PQR's and WPS's. You can put them together as well, but, granted, depending upon the electrode, process, and welding parameters employed.
I just had this little debate with some... well, god complex inspectors, who lost their case miserably with the mountain of evidence to the contrary of their stand on needing a totally different WPS for every single position of every process and every joint, etc. Clause 3 and 4 with their commentaries and B2.1 and 'The Professional's Advisor on Procedure Qualification Variables' need to be carefully reviewed in the development of PQR's and WPS's. There are also some great articles by some hillbilly from the east coast in the IT on the subject.
Now, while anyone CAN write a WPS, very few can get it even close to right. To get ones that will really mean anything will cost you about $150-200 each. And, since you need to have one to test to, unless you have a copy of the WPS you welded to then those certs they gave you are really worthless. And once you have them, they are just as good for that joint in production so you already have a start on your WPS collection. Don't lose them.
He Is In Control, Have a Great Day, Brent