We do sell our bolts and screws and send them out to customers if they want to change them over. We have clear options for screws and bolts when anyone orders pickups from our website. If a dealer doesn't have the exact model you want in stock, you can simply ask them to order the pickup and finish you want.
Yes, we're very careful with letting people do work to our pickups because we couldn't possibly keep a lifetime warranty on something people have taken apart and adjusted themselves. This is why we offer to take a look at any of our pickups if you feel there is any issue with it. (Although we don't mind anyone changing to screws or bolts we've supplied, to ensure they are the right size)
In regards to the tonal qualities between screws and bolts, technically, our screws are made with electrical steel so are extremely magnetic which we have made specifically for us, whilst the bolts are a machine steel/hard steel. This means the screws will have a little more output and clarity in comparison.
I hope this helps.