I've released Modifier Modifier Plugin 0.1.
It is available via the plugin manager. A plugin website will not be up until later tonight.
This plugin provides key-bindable actions for toggling modifiers for the current method, field, class, parameter, and variable, including synchronized, final, and static, as well as for cycling through possible access modifiers (private->(default)->protected->public). It also allows the user to specify a preferred modifier order, and provides an action to reorder a modifier list.
This plugin is not very mature and does not yet do three things that a plugin like this should obviously do:
1. Provide an intention to reorder modifiers according to your preferences
2. Provide an inspection for missorted modifiers according to your preferences
3. Allow you to select a series of fields/methods/etc. and change their modifiers as a batch operation
These things will come in a later version.
The actions this plugin provides are called "Toggle xxx" and "Re-Order Modifiers." To use them, bind keys to them, and then simply place the cursor anywhere reasonable on the line (before the parameter list, the open brace, etc., depending on whether it's a method, class, or what) and press the key.