"Perhaps in future years that same process will create the $100 PFD payment."
At which time a veto would be appropriate and timely instead of this one which effectively works retroactively.  My copy of a citizen's guide to the AK constitution may be a bit old but the comments on this includes, "A governor's veto might block a future legislature's effort to repeal a dedication."  Gov. Walker did that except in reverse, blocked the legislature from honoring a dedication protected by the Constitution.

"I am not comfortable that other areas of spending won't be "constitutionally protected" if you prevail."
The AK constitution prohibits dedicating or "protecting" other areas of spending. Art. 9 Sec. 7.  The Permanent Fund is exempt. The governor's salary is set by legislation and not constitutionally "protectable."  AS 39.20.010 set it at $125,000.  Electing to return or cut his own pay check is a different thing from vetoing and thus cutting/taxing thousands of Alaskans' PFD checks.