When in doubt, always check the Ethics text in your books I think. As I’m sure you know by now they have dozens of examples in Standard VII:B that go into (obnoxious) granularity about what is/is not a proper reference of candidacy/participation in the program.
As far as adding leverage to a resume Passed Level I = Level 2 Candidate. A Level 2 Candidate is the same thing as someone who passed level 1 but has enough money to register for the second exam. Essentially meaningless.
As far as how you should dictate it on your resume. Since you passed level 1 for now put “Passed CFA Level I”, once you register and pay for level 2 you can put “CFA Level 2 Candidate” if you wish.