First and always, make sure to confer with your department administrator regarding internal deadlines and processes that assist you in meeting campus requirements.
Note: Employment actions must be future-dated. At minimum, paperwork needs to meet deadlines for the Dean's Postdoc Action Report cycle that preempts the start date. Minimum lead time is two weeks or better. 
PDO Deadlines FY2012.pdf
Salary changes
- If you want to increase a postdoc's salary, look both at the processes -- there are two of them (annual and off-cycle), and the salary levels the campus has adopted.
- For any change in salary, there are also justifications or reasons to be used, especially in fiscal year 2010. Feel free to contact the PDO Coordinator, Valerie.Saltou@ucdenver.edu 303-724-2930, at any point with any question. Salary increase process
Current salary/stipend scale: UCD Postdoctoral Stipend-Salary at Initial Hire.pdf
Other changes
- Some changes are significant and require paperwork. One example is for a percent change of 25% or greater, or for above or below 50% time (affecting benefits).
- Others are not as labor intensive. See the differences here under "Job Data".
Making changes in the position or employment status