I've been playing in an online campaign with friends for a bit now and my character recently got their hands on a haversack. As a rule, we have in our group the haversack's capacity is greatly increased as to be worth the upgrade from a bag of holding (It holds double the amount). So the question is: How do i homebrew a container or make a copy of the haversack and increase its capacity/values?

You cannot, at least not currently. You can simply add it to the character sheet however, and customize it’s carrying capacity there to whatever weight your table has as the houserule.

Thanks for the help.... it worked!