I have heard that there is a new update coming this weekend for 2x chance to get mythic/arcane items in chests. Sounds good!

My big question is will this affect the chests already found or chests found after the update? Many people will be buying locked chests like crazy this weekend looking for mythic items. I am under the assumption that what is in the locked chests will not change when using reroll elixirs or luck pendant.

I guess I am just wondering if it would be a waste of money buying locked crates to open after the update? Or should I just open the ones I find instead?