Oldschool- In general Actors with their name above the title are considered leading, and those below the title are considered featured. For many shows the producers ask the Tony Committee to consider changes (In Angela Lansbury's case she is obviously above the title, but she performs a featured role). The committee meets to consider shows in bunches a few times a season.
The entire cast of Ragtime was below the title, but the producers asked for those 3 to be considered leading (possibly more but they might have been denied).
The producers can also ask for other changes. For example the recent Sunday in the Park with George had projections (usually considered lighting) that the producers asked be voted on for set.
David walked into the valley
With a stone clutched in his hand
He was only a boy
But he knew someone must take a stand
There will always be a valley
Always mountains one must scale
There will always be perilous waters
Which someone must sail
-Into the Fire
Scarlet Pimpernel
