The bolt that goes through the lower end of the rear passenger shock is stripped and I was wondering is it a bolt that I’ll have to replace or is it welded to the suspension?
It's not welded.. use a mallet or a hammer and it should come out. Just grab another one from toyota.
Get a new bolt (part #16) and nut (part #17). 2007 Toyota Prius Parts - Camelback Toyota Parts - Genuine OEM Parts - Free Shipping
I don’t think the bolt is simply removable. If that’s the picture from your Prius it doesn’t look bad. Just use a thread chaser (thread die) to go through it and it should be fine. That’s not the correct bolt and nut! Those attach the rear axle beam to the body. OP is talking about the nut and bolt that connects the rear coilover to rear axle beam. Here is the diagram that shows the correct nut: Каталог запчастей TOYOTA и LEXUS The correct nut has the part number 90178-14004.
A new nut should come with the new rear shock. I agree with valde3 that the OP should try to repair the stud threads if possible.