A tweak is a manual change in the file "XYplorer.ini", XYplorer’s main settings file. It’s easy to do, you just need a text editor:
IMPORTANT: Do not create the key but look it up and edit its value! If you cannot find the key then your XYplorer version does not support the tweak.
For example, you want to edit the key SettingsWarnReadonly. This is the original line:
SettingsWarnReadonly=0
After your editing it looks like this:
SettingsWarnReadonly=1
Save the file in your text editor.
Why those tweaks? A number of XYplorer settings don’t have a GUI, i.e. they are not featured in the Configuration dialog or elsewhere in the interface, mainly to keep the application smaller and easier to use. Those settings are called "Tweaks".