Hmm, H&K customer service has been great to you too, eh? Yeah, my USP-40C was bought used, came missing a few parts, called H&K about it, offered to PAY for the part for this USED gun but they still sent me out replacement parts for FREE and had them within the week! Stories about H&K poor customer service and "because we're HK and we hate you" are nothing but BS spouted by the haters! Everything I have seen first hand says the opposite!!!
Now as far as swapping out the safeties, it's not as hard as some people have made it out to be. The hardest problem I had was trying to read the poor photocopy of the USP armorers manual I had. Now this was back around the mid 90's when I swapped out my standard safety lever for an ambidextrous lever so I would think that a search on Youtube might have some results on doing this job. Again, haters will scream that the USP is complicated and you need to have an engineering degree and what not to work on them but again, that's just not so. While they are a little more in depth than a Glock, they're not the complexity that many haters will make it out to be.