Replace "Renew when replace" nuts and bolts or not?

There are different reasons for the bolts being "Replace and renew".

Some actually are stretch bolts so really do need to be replaced for example the engine mounts.
I know of very few indys that replace them and you do occasionally hear about engines falling.

Other bolts (subframe) aren't stretch bolts but are replace and renew because they're a steel bolt going into an aluminium housing. They come with a special coating on to prevent corrosion between the two, which is supposedly damaged when you remove them. As long as you coat them again in a suitable corrosion barrier I've never had any trouble.

None of the subframe bolts are stretch bolts, they should be threaded all the way.

If you already have them I'd be tempted to put them in. You'll probably be charged a restocking fee when returning them.

Sometimes you get stretch bolts or bolts with a deformable thread which are a good idea to replace. I've also seen ''single use" bolts that way purely because they have some threadlock on from the factory. I'm not cynical enough to think it's a scam, noone is getting rich from selling a few bolts but it could be extreme risk control, you could, after all, just put some more threadlock on.

Yes, recoating bolts that you should only "use once" because they come with locking paste on them is fine in my book, but I can see why VW Group and/or Haynes will list them as "use once" as if you don't understand that they started life have a locking paste dip, then things might not be good enough.
What has confused me in the past is where "use once" bolts have been reused by a VW dealer, and recently by a "good" indie on the engine mounting bracket on my daughter's late 2009 Ibiza when it was in for a "belts etc" change - I might need to buy some new ones and replace the old ones!

One thing, with my local VW dealer, when, under warranty they removed, examined and greased, then refitted the gearbox top mounting on a 6C Polo, they refitted the old bolts - but when I took it back in to get them to replace that failed bonded rubber mounting, all the bolts were replaced - I demanded a completed job sheet for both attempts to fix that as that car is our property and we are entitled to know everything that has been done to it within warranty as well as outside warranty paid for work.