Once the prop 1a funds are spent then the state can bank whatever it likes.

Some Prop 1a requirements that will block a Burbank to LA Union transfer of funds:

(2) the need to test and certify trains operating at speeds of 220 miles per hour

2704.09. The high-speed train system to be constructed pursuant to this
chapter shall be designed to achieve the following characteristics:
(a) Electric trains that are capable of sustained maximum revenue operating
speeds of no less than 200 miles per hour.

(3) Eighty percent (seven hundred sixty million dollars ($760,000,000)) of
the amount authorized by this section shall be allocated upon appropriation as
set forth in this section to eligible recipients, except intercity rail, as described
in subdivision.