[mothered]

I've got the replacement item, however I've made an error and there is a difference of about 350 grams (450 vs 800) between the items. Do you have any ideas on how to increase the weight of the package?

If an Investigation Is opened and the weight Is cross-checked, the difference Is significant enough to decline the claim.

The only thing you can do to Increase the weight In transit, Is add extra packing.

By the way, I know that this is kind of stupid in theory. However I believe that the Amazon workers in my area don't really care enough, so I hope for a successful outcome because of the amazon workers' apathy. I probably shouldn't rely on this, however this is the most convenient option for me.

I wouldn't personally rely on the probability of the worker's Incapacity to handle returns accordingly, but It's your SE and your call.