As someone who is dealing with budget spreadsheets right now for a business under a big corporation, and obviously these could differ...
but likely they send Disneyland a budget for the entire year, broken down by the quarter. In that they won't have necessarily separate categories for "Castle Roof Refurb" but just a budget for Repairs and Maintenance. Or Refurb in general. The management then would decide what they use that money towards on a local level, such as fixing the castle roofs, or replacing all the trolley tracks etc.
Now these could be given separate budgets and not even be part of the budget handed down, or it could be added to budget I guess, but projects like this may just fall under the main budget, and if they can fit it into the money they've allocated, they will...
But I would assume it would take it coming from a local level to decide that is high enough priority to use a chunk of the budget up for it.
Obviously huge expansion/new rides have the higher ups involvement, but projects like this would really be decided upon on a local level from the budget they've been allocated for the entire year or quarter.