The only way I have found to revert the game's ItemManager stack sizes to the vanilla values is to remove the plugin and restart the server.

Can you please make it so the plugin saves the vanilla stack sizes to a backup file every time the server starts, before they are modified? This way the vanilla backup will be updated when FP adds new items to the game. Then add a feature where the plugin can revert ItemManager stack sizes to the vanilla values from this backup file. Maybe even a config option to revert stack sizes when the plugin is unloaded.

This feature would make my life easier because I use MagicLoot, which reads the stack sizes stored by the game's ItemManager and uses them to determine the random size of partial stacks added to loot containers. For example, if I use StackSizeController to change the c4 stack size to 50k, then when MagicLoot adds c4 to loot containers it will add a randomy sized stack of c4, anywhere from 1 up to 50,000 items! Obviously I can't have players getting 34,890 c4 from popping one barrel!

My current solution is to remove StackSizeController and restart the server, then load MagicLoot and get it to generate it's private stack size table, then install StackSizeController and have it increase stack sizes. I'd really like to be able to do this without restarting the whole server!

/stackall default sets the stack size to a default specified in the config file, not the vanilla size.