You can absolutely bid for vacation.
You can also choose not to bid. The company will randomly assign your maximum vacation days...Upon your return, and within 30 days, you can cancel the awarded vacation and either bid monthly or have the vacation days moved to any vacation period awarded to a junior pilot. You can reference the vacation award announcement on Flying Together to shop for your desired dates.
I emailed the company and got my vacation moved. Worked like a champ.
Ref: MOU 24 (page 637 of the UPA)