.. one additional question:
can we change item prices in a way that won't be overwritten with the next update?

Originally posted by @waspoza in #6 (comment)

Thank you very much! ❤️

The intended way is by crafting a pricelist plugin as a separate companion addon to BastionLoot and distributing it to your officers and optionally to members as well.

Since this requires some minimal familiarity with wow addon file structure and Lua most of the documentation can be found in source comments at the example-plugin + (source)

After the plugin addon is customized to your guild and installed.

The guild leader can pick it in [Select Price Scheme] option of BastionLoot.

The name of the new price scheme can be added at the bottom of the Guild Information text (not the GMoTD)
with the format of {schemename} curly braces enclosing the schemename exactly as it shows on the Select Price Scheme dropdown.
This will ensure that every member that logs in with the plugin installed will use it for gearpoint price information regardless if they were online when the GL changed the pricelist source.

The GL can also use the [Share Settings] button in BastionLoot options to push the option to guild members but this will only update members online at the time.