Database changes would include adding a column "is_type" to "phpbb_acl_options".
File changes would be adding a boolean
$is_type to the auth::acl_set() method. This value would determine the "is_type" column. Also if it is true a
a_[color=#FF0000]$prefix[/color]auth row would be added. If a value is_type, it would automatically add a role system, and add it to the drop boxes for permission types.
Of course acl_delete would undo this.
If phpBB will support this way of adding permission types without editing files it'd encourage more mod authors to use a new type for their mod, which will make the ACP permission system easier in use. (If you have like 5 mods installed, all adding new permission either to tabs or in already existing tabs, your rows will not only be huge and force you to search the right permission you want to adjust, but also it'll make the vertical space taken of the tabs bigger then the page width and mess the style up that way.