Making changes to game systems in Foundry?

[Yora]

I got the D35E game system for Foundry and it looks great. Now I want to make some changes to it, like deleting character classes and monsters that wouldn't be available in my game, and perhaps even editing the XP values needed for each level up.

But when I unlock a compendium to make changes on it, it shows a message that any changes to compendiums from a game system will be lost when the game system updates. Of course I don't want that.

What would be a good way to customize the rules for my campaign and keeping the changes when D35E updates?

 

[ShadowAssassin]

Make a compendium with your own stuff as that won't get overwrittyen when updating.